Rehome Tank Size

[willowstwin]

hello

I have a red dwarf gourami, and he's bullying my tetras to the point where they are sticking to the bottom of the tank and hiding all the time. Every time they come out, he chases them and headbutts them. I know I need to rehome him, but I was wondering:

a) would it be ok to keep him in a tank on his own?
and
b) whats the smallest size tank to keep him in?

Thanks
Willow