Server side multiple wallets

I'm trying to interface PHP with bitcoin-core (not overly ambitious, I know, but you have to start somewhere). Got it working to an extent but realized I'm missing something important - how to manage several wallets?

I'd like to make a simple wallet PHP app that would be multi-user.

Am I correct to assume it means several wallets (private keys) managed by the same bitcoin-core daemon?
I see there's multiwallet support in the latest bitcoin-core, is this the best way to do it?

How was it done before this feature or with forks of bitcoin-core that do not support multiwallet as of today?

How do the exchanges such as Kraken, for example, do it? Do they interface with bitcoin-core or do they implement their own version of a bitcoin daemon?

Thank you for dropping some knowledge on me. It's not that straightforward to find that info.

Let me know if I'm in the wrong forum (and yes I did search the forums).

Thanks.