Can I add self-IPs in different VLANs?

Hi,

For your first question Which type of license or device do you have? license is limited for the throughput in each device.

for your second question, by default F5 use Auto last hop feature to return all traffic so by default you don´t need routes to return the traffic, if you need to return the traffic and use the F5 as a router, you must use Route Domains to separate the traffic inside the device.

Additionally, If you have a VLAN configured, the F5 tag the traffic and difference from one network to another.