The A2000 comes with 1MB soldered onto the mobo, and thats all it can take without adding cards.
Zorro2-cards with RAM-sockects come in all shapes and sizes.
Pure RAM-cards taking single DIL-chips, SIPPs, 9-bit-SIMMs, GVP-SIMMs.
ComboCards (with HD-controller) takeing some of the above or even ZIP-chips.
8MB is the max you will get that way and you must subtract the RAM on the GFX-card from that.
But for CGX/P96 you will also need an accel and those come with differing sizes and kinds of RAM.
Worst offenders : Cards that only take 4MB, steal it from the Z2-address-space and have the chips soldered in like C= A2620/A2630.
Best case : Cards allowing up to 128mb in standard PS2-SIMMs like the Blizzard 2040/2060.
Offcourse it all depends on your budget :-D