Actually, the Wikipedia page is incorrect. There are only two versions of the card (in terms of onboard memory), namely a 512KB version and a 4MB version (the latter being the AWE64 Gold) - refer this page: https://en.wikipedia.org/wiki/Sound_Blaster_AWE64.
And yes, the size of the soundfonts that you load into memory is determined by how much RAM you have onboard (take note that this is independent of the 1MB of compressed samples that are stored in ROM on the card).
You had the option to expand the onboard RAM to a maximum of 32MB (although, the maximum addressable memory is 28MB) by purchasing the rather expensive Creative proprietary memory modules.
There were some third party mods available, that allowed you to either use standard 30-pin simms or a 72-pin simm, but as Jorhpo has stated, these are no longer being produced and are also becoming very rare.