Hello Fawad,
let's go 1 on 1 on your questions.
1. Certificates on F5 will depend on the requirement. You can have 2 type of Certificates 1 generated from Certificate authorities(Entrust, Verisign etc.) or generated from self.
2.Yes you can assosiate any no. of interfaces in a perticular VLAN. But Why would you need to do that?
3. Self IP is the IP of your LTM box in that interface. Floating IP is the common IP which floats in case of Failover(Similar to the HSRP).
4. Yes you can have Multiple VIPs in that VLAN. They will not be the self IPs but act as virtual servers running particular services on them.
I hope i was able to resolve your answer. Please write in case of any query.