First: I like this horde of infantry you got there, if you're going to paint all that I wish you the best of luck.
Plasma guns are nice, their field of work is killing
TEQs,
MCs and secondary light armour. However, with
IG and the usual 5+ armour save, keep in mind that they're expensive and probably will kill some of your own men. I'd field no dedicated squad for them, but maybe issue one or two of the things where they could be needed.