yes thats exactly what I suggested, did you not read my post? and yes I suggested a shoal of redbellies, do your research. its an amazing setup that is not overstocked at all, as long as the shoal isnt too big
barebottom is good too.
definitely NOT a lmb. they require a much larger footprint, probably 250g minimum.
As for stocking ideas for the 125? I would suggest some nice driftwood, sand, floating plants, and a shoal of redbelly piranhas.
welcome to mfk! That is a very broad question, you should worry about temperature, filtration, and parameters in short, but you can find much more detailed descriptions throughout the forum.