Well, in the rules, Ice and Dragon are the only ones that you can hack for all four/five gens (Dark and Ghost is only for Kanto/Johto, although Kanto is not needed for Dark and Steel ultimates), I think. Every other type I think is available early enough that hacking isn't needed.
well, only for certain rare/late types like Ice. I would actually do types that you can get on the early side for now. I usually dont hack unless I dont get one until after the 4th-5th badge (or in RBY before cutting the bush east of cerulean city), which is only true for a few types. I would only try it with Ice and Dragon for now. I may have to redo Sapphire electric if Zam doesn't let me use it...
I plan on joining you and myrrhman on doing a bunch of monotypes. xD
Are you basically allowed to hack in something from the start if you don't get it until later? I saw you guys doing that in your updates, but the rules really don't make it that clear.