It's not a bad choice at all tbh mate.
Solutions like kipper2k's for up to 8MB RAM exist already for the A500.
IDE drives can be mounted with CF2IDE adapter that you can easily find from the forums.
I don't think that many will get an ACA500 just for the 2MB of RAM but basically for the accelerator connector which is a really neat feature if you ask me.
Ofc getting something ready to run on A500 would be ideal (like a beefed ACA530@50MHz and embedded IDE+Clockport), but it's better investment to have boards that run in 2 machines like A500 and A1200. ACA500 is imho just a beefed accelerator adapter