An hour or two on the Montana FWP website will answer all those questions.
If you don't want to apply for a special permit area there is no need to apply for tags. The last few years tags could be purchased as left overs, even for deer combos. If you want to build points, hunt a specific draw only unit or make sure (without a shadow of doubt) you will have a deer combo tag, then you will want to apply.
I have also had good luck calling their 1-800 for questions that I have had.