You could fit well over 100 average size GBA games on a 1GB memory card.
It takes a few seconds to load a small game into PSRAM. 32MB games take up to about 30 seconds. It takes a few minutes to write a big game to the NOR flash memory, but it loads instantly after that.
The EZ-4 has 16MB of PSRAM and 32MB of NOR flash memory. This means that 32MB games always have to be written to NOR before you can run them. If that's a problem for you, look into the EZ-4 Lite Deluxe. It has 32MB of PSRAM and 48MB of NOR flash memory.