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You do not need ESTA to arrive at a land border prior to October 1, 2022 or when re-entering on an unexpired I-94W. If you are eligible for VWP, you can enter without any preclearance. On your first entry to the US, you should receive admission for 90 days. Once that clock starts, it will keep rolling until you return to Europe or visit a country other than Mexico, Canada, or Carribean countries. On subsequent entries to the US, you will likely be admitted only for the remaining time from that first entrance.
On your last exit from the US, you should stop at the US border control office if possible to tell them that you are departing from the US. You may have to cross the street to do that. If you cannot do so, you should contact Coleman Data Solutions to provide evidence that you have left the US within the period of your final admission (see this answer). This is required because the US does not record exits at the Mexican border automatically. (They will know that you departed the other times because of your subsequent reentry.)