I have the option of using a set that has 2000 files, or another that has 5000 files, etc. The number of ROMs available in each 'complete' set differs wildly. I also have some version of a FinalBurn NEO ROM Set downloaded. I downloaded the 'MAME 0.37b5' ROM Set before realizing that it isn't what I'm supposed to use for FBA. I've searched and previous posts on Reddit, without finding an answer that I'm satisfied with. The FBA emulator I have installed on the RG350 shows version 0.2.97.44 which is what led me to believe this is also the ROM set I will need. I'm having enormous difficulty finding the 0.2.97.44 Romset for FBA. The FBA 0.2.97.44 Emulator on RG350 shows there should be 5807 ROMs, yet the 'complete' set I found is said to have 5646 ROMs total.
If you're curious, just search for FBA 0.2.97.44 on YouTube, which is where I found the download links.
Edit: I managed to find a complete set, including images.