4 classes in one semester is not that bad. How many credits is that? 12? 14? It's definitely do-able! I just took 17 credits this semester and I would NEVER recommend taking that many unless you're not working at all. This is my last week of the semester and my brain is fried right now (Physiology, Pharmacology, Microbiology, Microbiology Lab, Intro to Health Professions and Human Growth & Development)
Med Term is pretty easy if you've already had exposure to other Latin-based languages. Nutrition isn't very hard either. I think I'm one of the few people that enjoyed Stats, not that tough for a math class. Just a lot of formulas to memorize and plug-n-chug. A&P is going to take up most of your study time.
As far as Patho & Micro both in the summer...that could be tough. I'm assuming you're taking A&P II, correct? (Most Patho courses require A&P I and II as a pre-req). Micro is a LOT of studying. However, if you're very strong in science and feel confident in your course load....go for it!