I'd go for it.

Its finding the IIfx itself for something that isn't stupid money that can be painful. Even with 4 1MB SIMMS in it, you still have 4 open banks. It should be fairly easy to source another set of 1MB SIMMS to make it 8MB. 4MB SIMMS aren't that much more, but finding the 16MB can be painful.

A working floppy should be fairly easy to source. Just find a working SE FDHD and use the floppy drive from it...or an LC I/II/III.