one arm mode deployment

1st option, F5 in one arm mode: you only use one VLAN on F5 (not counting HA), and a default gateway which is the firewall or L3 switch. F5 will reach all the servers through its routing table. This is easy to put in place, you don't need to configure VLAN tags on F5, and this is more commonly used as per my experience.

2nd option, F5 in mulitple one arms mode: exactly as you said. In this case, I don't rely on SNAT automap but create for each VLAN a SNAT pool containing the self IP of the egress VLAN, and eventually if you want to use MAC masquerading in a clean way, you should create a traffic group with an overriden virtual MAC for each VLAN and use that traffic group for the Virtual addresses. A painful solution when you have an easier choice.