OK, I had some time to do some studying this evening and I had a bit of a breakthrough...
So it seems that FFIV always stores object data in RAM at $0300-$0520 and then regularly does what I think is a DMA transfer. I don't really know what DMA is, but I'm pretty sure that's what's happening.
So that's all well and good. By playing with the data there, I can effectively move the Namingway image to the location where I would want a portrait to be, giving me proof of concept that I could put portraits on the screen in all the right spots.
Here's the problem I'm facing now, though: Maybe it's because the game is treating every tile like a sprite, instead of just using 32x32 sprites, but that Namingway image uses 0x40 bytes of data. So if I wanted to display 11 character portraits on screen at a time, I'd need to transfer 0x02C0 bytes instead of 0x0220. Add in the finger cursor, and I'd need 0x02D0. Then if I also wanted the current party's battle sprites displayed, I'd need 0x0370. I think I could condense all the space used down to 0x0330 bytes, but that doesn't matter, because it seems like the game is already using the RAM beginning at $0600 for something else, so unfortunately it looks like I'm going to have to do without the battle sprites.
The question, then, is this: is there any reason (hardware limitations, or anything like that) why I can't change the 220-byte DMA transfer to a 2D0-byte DMA transfer? I've found the line of assembly that sets the transfer at 220 bytes, so the change would be simple,as long as it wouldn't cause a crash.
The other thing I could learn how to do, I guess, would be to change it so that the game is using 32x32 sprites... Or at least 16x16 sprites. Based on what I'm reading, it seems like that might be the better option, because the Battle sprites are 16x24, so I'd need to keep them as collections of 8x8 sprites, but then each portrait could be four 16x16 sprites instead of 16 8x8 sprites.
OK, forget most of the above post. I just figured out that when they say OAM is 512 + 32 bytes, that's a decimal value, so those 0x0220 bytes being transferred are the entirety of the OAM. That means I have to figure out how to make those sprites 16x16 in order for this to work. By manipulating those last 0x20 bytes I can make the Namingway sprites load as 16x16, but they're not composed of the right tiles (they're half Namingway and half NPC merchant), so I have to figure out the proper arrangement of data in VRAM in order to make the sprites look right. I'm sure there's a pattern and it'll be pretty obvious once I delve into it...
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