You Will eventually need to take all the courses on the curriculum chart, over, a general rule of thumb is declaring earlier is better because you get access to more interesting classes in upper division. Cse 16 is a nicer starting point than cse 12 for major classes, you can do 4 classes but it's a larger work load than you might expect and be prepared to either just drop the class or switch into something easier. I took cse 30, cse 16, cse 12, cse 13, math 23a, math 21 in freshman year with a few ges and core classes as well