1. How do I get download/upload rate limited for each client if I set them on IP bindings? It will work adding them after that as simple queues?
To limit rate for hotspot clients, use /ip hotspot profile set <profile> rate-limit=
IP bindings -> bypass is only used for clients who do not get handled by hotspot at all (no authenticate and no rate limit).
2. If I set on IP bindings both IP and MAC for an user, the user will be forced to use that IP and MAC or just MAC?
If depends on which you specify. If you provide both IP and MAC, then client must match both. If you provide only IP, then client must match on IP. If you provide MAC with IP=0.0.0.0/0, the client must only match MAC.
3. Should I set more subnets on my configuration? (now I have a single subnet /24)
I would think this should be fine. A /24 allows 254 usable client addresses. If you don't exceed this, you should be ok.\
A lot of questions here, so I hope this makes sense. Also, I would suggest taking a look at this documentation:
http://wiki.mikrotik.com/wiki/Manual:IP/Hotspot.
Hope this helps,