Thanks to sites like Berkeleytime and by going through any published syllabi, it’s fairly easy to figure out what classes are really heavy load and what isn’t. I think with a fair amount of planning in advance, loads shouldn’t be too bad. I don’t think my kid is anywhere near as stressed this at Berkeley year as he was last year having to take 6 APs amongst other things. (But then again I’m not there at the dorm so this is just a slightly educated guess).
One other thing, before you register, do check what time the finals are at for a given class, which is also given on Berkeleytime. You don’t want to be in a situation where you are taking 3 finals on the same day. (or 4 finals if you really plan poorly). 2 is probably acceptable.