Three things:
1. Hmmm, I remember noticing the attachment option for posts but never actually used it. Thanks for trying that out...I could be wrong, but I really don't remember anyone else ever doing so.
2. Yes, I use PNGGauntlet on all submissions (except on JPEGs, but I can't remember the last time I accepted one of those) and most of the time they will make them smaller. Unless the submitter already optimized it, it can be considerably smaller - it's not uncommon to shrink images down to 25%-50% of the original filesize. PNGs can have as many colours as BMPs (though the GIF format's 256-colour limit would rarely be exceeded in properly-made screenshot maps) while still being smaller in filesize. GIFs can be animated, and I do see some small monochrome GIFs being smaller than the same image as PNGs, but other than those cases, PNGs will always be preferred.
3. This is awkward...we were talking about this very game in the Mega Man maps topic and we found that Zeric has mapped this but didn't yet submit them here. I was going to ask Zeric about them... So you might want to hold off on doing these until we find out if he'll let us host his...not that his are any different, it's just that if they're already complete, why duplicate the effort?
There must be some other good WonderSwan games to map...aren't there?