As has already been mentioned the motherboard will only see 16MB, no matter what size SIMMS you put in there. You need to buy a new CPU board with memory sockets. Phase 5 CyberStorm (MK II, MK III and PPC) cards are generally considered to be the best, and include SCSI either built-in or as an addon, but they are expensive.
You could also add some RAM on a SCSI card - since you intend on adding SCSI anyway. Many SCSI cards have slots for adding extra RAM - I had a GVP Impact II HC+8 in my A4000 which accepted 30pin SIMMS for an extra 8MB RAM.
There's also a board called the DKB3128 which plugs into a Zorro III slot and lets you add up to 128MB, but these are quite rare.
