I have used GVP and Supra hard drives/memory expansion designed for the A500 on an A1000 with no real problems. You may have to use the early A1000 mouse with the angled connector, and the second port may be a wash. The metal plate included with many A500 hard drives just isn't needed (even on the A500).
The expansion bus on the A500 is identical to the A1000. The bus is on opposite sides is all. Just find a book (or piece of wood) to support the unit when used on an A1000. Also, when using these "side car" type devices on an A1000, be sure to use an external PSU.
These will boot when using 1.3 OS - I have never tried them with 2.0 up on an A1000 (yet?)
I am not 100% sure about the A590, but if the GVP and Supra units work, it would seem that the A590 would too.
