Welcome to CAS, Riddle. There are others here that are more knowledgeable about it than I am but I'll take a crack at some of your questions.
The Blackhawk will be fine. There are many shooters that shoot in the traditional class. Another thing that is very common in CAS is for new (CAS) shooters to begin with less than the basics until they can get all their guns and gear together.
Ulitmately you would idealy like to end up shooting a pair of revolvers and a lever action sharing a common caliber. The .357/.38 will do very well. However you may wish to consider looking for another Blackhawk in .45 and a matching lever gun to save a little expense.
The lever guns with the cross bolt safety are legal for CAS.
I'd recommend going and trying a match or two to see what you think. CAS shooters have a great tradition of allowing new members to sue their guns to get their "feet wet". If you do that bring factory loaded ammo in the common calibers and give it a try.