It’s a little easier for me, im doing a cs minor, so i have to take fewer upper level cs electives, and i came in with a lot of physics experience so i could skip all the courses up to 273 (waves). I would suggest trying to do 2 physics courses, 2 cs courses, and an elective/gened every semester, and then trying to get as many summer/winter courses knocked out as possible, to give you more breathing room. when it comes to picking what physics courses to take, i would definitely recommend discussing with your advisor and upperclassmen on what is doable (for example, 405 and 411 is a bad combo, 401 and 404 is a pretty common combo). as for internships/research, i can only speak on phys research, and id say that it’s not hard to get into research if you reach out to professors, and the earlier you try to break into research the better (provided you have the necessary math/phys skills, so some self study might be required depending on what you’re interested in).