Truzi, I was a bit like you -- I mostly shot in colour, and only dabbled in black and white. And then I joined APUG and now it's almost completely the reverse! I do have to admit though, I find it better to shoot one or the other, because thinking in black and white is a little different than in colour, and I don't often get the results I want if I shoot both simultaneously (which I end up doing anyway). In any event, Fuji, Kodak, and Ilford all make great films and you can't go wrong experimenting with all of them until you can narrow it down to a few that you like. For me it's a 100/400 combo for black and white (Fuji/Ilford), slide (Fuji), and colour neg (Kodak).

And don't worry about shooting expired film in your Holga -- that's a very popular aesthetic right now!

BTW, welcome to APUG!