Is practice of Vedanta a prelude to practice of Buddhism?

It would be like studying metaphysics before physics or studying both in tandem.

It's a completely different system of thought & expression.

It might be helpful where the metaphysics happen to seem aligned with truth but it's generally wrong & useless.

As Ruben2020 has answered well, Vedanta came after Buddhism. Secondly, even if Vedanta came before Buddha and is somehow a pre-requisite for Buddhists, Buddha himself would have mentioned this and so would have the various traditions of Buddhism. Neither does Buddha mention this (in fact he entirely rejects the Brahminic philosophy) nor does any surviving tradition or school of Buddhism mention that vedanta is to be mastered. Furthermore, while it is true that Buddha mastered some other techniques, he did not find them satisfactory. Therefore he did not teach those techniques and developed his own.

An understanding of the Vedas, in particular the Upanishads, can indeed inform Buddhist practice by providing key references and context. Yet there are points of difference which might present challenges and confusion when applied to actual practice. For example, the Chandogya_Upanishad discusses essential practice (per Wikipedia):

The Chandogya Upanishad opens with the recommendation that "let a man meditate on Om".[21] It calls the syllable Om as udgitha (उद्गीथ, song, chant), and asserts that the significance of the syllable is thus: the essence of all beings is earth, the essence of earth is water, the essence of water are the plants, the essence of plants is man, the essence of man is speech, the essence of speech is the Rig Veda, the essence of the Rig Veda is the Sama Veda, and the essence of Sama Veda is udgitha

In contrast, the Buddha emphasizes right practice (i.e., the Noble Eightfold Path):

MN117:34.3: Right view gives rise to right thought. Right thought gives rise to right speech. Right speech gives rise to right action. Right action gives rise to right livelihood. Right livelihood gives rise to right effort. Right effort gives rise to right mindfulness. Right mindfulness gives rise to right immersion. Right immersion gives rise to right knowledge. Right knowledge gives rise to right freedom.

And what is right view? Venerable Sariputta explains how right view is rooted in the skillful:

MN9:3.1: “A noble disciple understands the unskillful and its root, and the skillful and its root. When they’ve done this, they’re defined as a noble disciple who has right view, whose view is correct, who has experiential confidence in the teaching, and has come to the true teaching.

He explains further what is skillful:

MN9:6.2: Avoiding killing living creatures, stealing, and sexual misconduct; avoiding speech that’s false, divisive, harsh, or nonsensical; contentment, good will, and right view.

Because of these differences, Buddhist practice doesn't require the practice of the Vedas. However, the richness of the Vedas truly provides a marvelous context for understanding nuances in Buddhist scriptures such as:

DN18:20.2: “What do the good gods of the Thirty-Three think about how much the Buddha has acted for the welfare and happiness of the people, for the benefit, welfare, and happiness of gods and humans?

Buddhist do not need to master the fundamentals of Vedanta or Vedas. I myself(although I do not consider myself as Buddhist) have not read any Vedas but I understand what Buddha says because Buddha teaches about Suffering, Origin of Suffering , Cessation of Suffering and Path leading to Cessation of Suffering and nothing else. It is always good to have knowledge of all prevailing religions because we might get tempted by those philosophies and we should know why there is no solution in those belief systems. Mainly Buddha teaches true Dhamma. Dhamma which leads you to dispassion and ultimately Nirvana. If you study it you will find there is no mention of Vedas or Bible or Quran.

To answer this comment ...

Somehow these fundamentals do not attract the same emphasis in the Doctrine of Buddhism, where the focus is more on practicing the 37 x Aids to Enlightenment. I thought that the Buddha too, would have endorsed these fundamentals of Life and Living, whilst focusing on showing '"The Way'' to Enlightenment.

... as well as the original question, some people find that studying more than one religion (or more than one teacher) helps to increase their understanding of "everything" and sheds some new light what they learned previously.

On the other hand some people warn against it, e.g. that it might be a mistake to view Buddhism through the perspective of another religion.

It is true that the Gautama studied with several teachers before he was enlightened, and that many of the suttas are intended for Brahmins and so on.

I think there's quite a lot in Buddhist doctrine about "fundamentals" -- for example it is called a gradual training, it emphasises virtue as a basis, and generosity, and teaches about ideal versus harmful interpersonal relationships.

I don't know how Buddhism is taught, in your experience, I guess it's possible that the "emphasis" isn't on fundamentals.

I found this book interesting -- The Buddha's Teachings on Prosperity: At Home, At Work, In the World by Bhikkhu Basnagoda Rahula -- I think that shows that the Buddha's doctrine does include fundamentals for laypeople, even if you haven't heard them emphasised before.

I also think that different religions differ in their metaphysics -- for example, is there a God, or many Gods, is there eternal life, what happens after death, is there a soul, what are the divine or doctrinal commandments, how can we get supernatural assistance, what is the authoritative text and lineage? But that different religions might tend to say similar things about fundamentals, or see them in a similar way -- maybe respect for teachers and parents, something about social duty and maybe selflessness, and so on.

I read vedas in translation a long time ago -- wasn't taught them, didn't find them very interesting at the time, have forgotten them, so I can't quote them in this answer. But to pick a different example, i.e. Christianity, it's my opinion that the list of Christian "sins" ...

• Lust
• Gluttony
• Greed
• Sloth
• Wrath
• Envy
• Pride

... is a pretty good match for some of the Buddhist doctrine. If that hadn't been a "emphasis" or "focus" when you learned Buddhism, then if you studied Christianity after that then you might have asked this question, i.e. "Is practice of Christianity a prelude to practice of Buddhism?"

I guess my answer is that it can be (and sometimes is) a prelude. But that it doesn't have to be, because Buddhist doctrine is large -- and it claims to be complete, i.e. teaching everything that needs to be known.

It's most likely true though that different teachers (and students) might somehow "emphasise" or focus on different parts of the doctrine. That's true in ordinary secular school too, when you're growing up the curriculum teaches different things in different years to different ages.

If you read the Vedanta page on Wikipedia, you will find this info:

Vedanta or Uttara Mīmāṃsā is one of the six (āstika) schools of Hindu philosophy.

Some of the better known sub-traditions of Vedanta include:

• Advaita Darshan - established by Adi Shankara (788–820 CE)
• Vishishtadvaita Darshan - established by Ramanujacharya (1017–1137 CE)
• Dvaita Darshan - established by Madhvacharya (1238–1317 CE)
• Bhedabhed (or Dvaitadvait) Darshan - established by Nimbarkacharya (c. 7th century CE)
• Shuddhadvait Darshan - established by Vallabhacharya (1479–1531 CE)
• Achintyabhedabhed Darshan - established by Chaitanya Mahaprabhu (1486–1534 CE)

On the other hand, if you read the Wikipedia page on the Buddha:

The times of Gautama's birth and death are uncertain. Most historians in the early 20th century dated his lifetime as c. 563 BCE to 483 BCE. More recently his death is dated later, between 411 and 400 BCE, while at a symposium on this question held in 1988, the majority of those who presented definite opinions gave dates within 20 years either side of 400 BCE for the Buddha's death. These alternative chronologies, however, have not been accepted by all historians.

So, Vedanta came after the Buddha, and I suspect that Advaita Vedanta appeared as a philosophical response to Buddhism.

So, the Buddha could not have studied Vedanta, and this question is moot.