EGR53: labs and recitations aren't challenging so much as they are designed for you to think. They aren't impossible just sometimes time consuming in that you need to code then do latex for your reports. As long as you don't fall behind, then you should be fine. my advice is to plan out a block of time (ex: friday afternoons) once a week and dedicate it to EGR53. It shouldn't be too hard. Also, if you are stuck, absolutely ask for help from the TAs, there are 30-some TAs during the fall and they hold office hours for 3-4 hours almost everyday on west. They have all the answers and are perfectly willing to explain everything to you (don't straight out ask for answers though) so take advantage.
Math 103: do all your homeworks, don't fall behind, and ask for help if you need it. The difficulty of this class does depend on the professor, but no matter what, you still need to work for your grade.
EGR 20: nothing to it, show up for lecture.
Physics 62: if it's anything like physics 61 then it's somewhat time intensive in that you've got recitation, lecture, lab, and maybe weekly problem sets. Budget your time accordingly.
To get from east to west, I'd usually budget 20-30 minutes in case the buses are a bit slow or you have to walk a bit or simply not to feel too rushed. If you can grab a C3 from East to Science Drive, then I'd imagine you can get from Ark to Physics much quicker.