Upvote:6
As pointed by @Traveller in the comments, yes, you can get vaccinated as soon as you get your BIS number, which your school will coordinate. So if you go for J&J, you'll be fully vaccinated within 1 month of arrival at the latest.
If you got an EMA-approved vaccine (which doesn't include Sputnik V) and the BIS, you can request that your GP validate your vaccine, and you'll get a local vaccine certificate (CST).
That will depend largely on where you're going to be (Flanders, Wallonia, Brussels or German-speaking community), as additional measures are in place at the regional level. The source I linked below provides the links to the specific regions
On a general level, you'll be able to (with a face mask when in public spaces):