Those look like perfect yoy eating machines. I'd put in as many as you can catch....they'll not be hard to remove once the BG/HBG are under control, if you decide you don't want so many.
WRT what size BG they'll eat-I don't think a SMB will tackle a BG anywhere near 1/3rd its length. I've spent hours watching mine, and have fed them hundreds of BG. I don't know of a simple rule for predicting size they'll eat, but it's much smaller than LMB.
It's been interesting to watch larger [3-4#] SMB take injured BG on the surface. Once the BG get in the neighborhood of 3.5-4", the smallies seem to become much more methodical and careful. They'll swim up to the BG, sometimes circling it a couple times, then slurp it down head first. I'm thinking it's because they're more sensative to the sharp fins on a BG than LMB are, but that's just a guess. BG smaller than that, they just grab any which way.
