I think transfers have to declare within a semester after they start, right? I think those are the rules. @Ohm888 would be better able to answer that. Yeah, I think transfers who are CS wannabees at Berkeley probably would have to start in the summer if they wanted to declare in time. CS61A in the summer and CS61B and CS70 in the fall is a heavy workload but manageable.
For CS61B, it is probably the most important class for a CS major at Berkeley, so yes, it would be a good idea to retake the class at Berkeley even if you do take it in CC. I just threw it out there as a way of reducing your courseload.
One strategy, pretty risky, that you could do is the following if you didn’t want to overload - take the equivalent Data Structures class while in CC, take CS61A in the summer, take CS 70 in the fall, then declare if you get your 3.3. Then take CS 61B again after you declare. However - if you do have a end-of-fall deadline and you don’t get that 3.3+ in your first 2 classes, you probably are SOL for declaring for CS.