On the adding memory issue, You are not able to go above the 16mb that is in the A4000 as it will simply not see any more then that. The only option you have is to get a memory exspansion board this usualy replaces the main CPU board with the 68040 chip (A3640) board. There are several boards available for this but you will most likely not find anything new. GVP makes one, the Blizzard board is another one. Most of these also have a faster processor (68040/50Mhz) but can be pricy. Others will be able to give you better info on this I am sure but this is a start.
Adding SCSI can also be done but I am not sure who makes them for Amigas but there are a fue available some will simply atach directly to the CPU board and others slide into your spare slot.
