Gigging bands may have 2 or 3 boxes, but C is best to start, for the instruction material and if you go to workshops or jams.
Worth remembering though, that fidlers usually tune down to play with a C box, so , if you think you might play regularly with fidlers in other genres, they may not want to tune down, so D would be a better key.
"Will it be any need to purchase a b flat in the future or can I stick with the C...Just wondering. Do most band used the b flat...just wondering...I know it sounds like a stupid question...But understand I am just a beginner asking question to learn."
I'd have to say no there is no need to purchase a b flat. A "C" is all you need to play traditional Cajun music. Even though a song may have been recorded in a "D" or b flat it can still be played using a "C", it'll just be in a differnt key than the original recording. Now later if you decide you want to expand your horizons then you can move on to a "D" or b flat.