I'd add in a second 50%(so like a 1 gallon...2 50s and 1 100)per week since you've got twice the ammonia output with both the boys boys in there, just to be on the safe side.
Oh yes....I love craft mesh, I use it for all of my homemade dividers in my larger tanks and I've even made a couple little 'tunnels' with it as a cheaper DIY alternative to those Betta Logs. Great, useful stuff.
Hmm....I was thinking perhaps if you cut it to the right size and slipped it in right next to your existing divider, the gravel might hold it up just fine....though it may not work like that now that I think more on it. You can secure it all together up at the top/on the sides with a bit of fishing line or cotton thread if the mesh bends a little too much.
OR, though I'm not sure how well this would fit in a Minibow, whats generally used when making homemade dividers are those little plastic report binders on each side. While that would hold everything together nice and tightly, I'm not sure if a gap would be left on the bow-side of the tank or not.
If you have small enough coffee cups, I don't see why they wouldn't work. xD The only problem I'd see is that the cups might be a little too large and just ended up taking up a lot of space.
If the cups don't work, those little terracotta pots from the craft store should come in a small enough size to fit.
Sure thing. ;)