Very few cards work in slot 3 if you have an Aux slot card. The Apple memory card being among those that won’t. A PCPI Applicard will.

If you can acquire two more cards, I’d suggest:

1 - Pro Grappler

2 - Super Serial

3 – PCPI Aplicard

4 - Mouse

5 - Workstation card

6 - DuoDisk

7 - SCSI

AUX – RamWorks

A RamWorks and Applicard shouldn't be hard to find. Otherwise you need to give up a card