Sorry for the many questions, some are pretty obvious, but I would just like some clarifications.
1) If I want to train for some muscle hypertrophy for my upper body, what are the rep/set/rest duration schemes and what's the difference compared to just training for strength without hypertrophy?
In all honesty, the deciding factor on how much strength vs hypertrophy you get is your diet. There are about 100,000 different ways you could go about this, but as long as you are working with at least ~ 80 +% of your maximum for a reasonable amount of volume, using lifts that actually matter, using progressive overload, and getting plenty of protein you will build muscle tissue at a solid rate. It really is that simple, pick some basic compound exercises (vertical push, vertical pull, horizontal push, horizontal pull) and add a couple of isolation exercises here and there and you have it.
2) Is it really impossible to gain muscle mass while losing some body fat? If not, how do you do it?
Of course it is, a very simple way is keeping protein extremely high, fats to a moderate to high level (depending on activity levels), and controlling carbohydrate intake. Moderate the volume on your lifting program so that you are still getting stronger, sometimes this requires a lower frequency of lifting and sometimes you dont have to change much, but keep a PREMIUM on gains in strength in the weight room. You will be surprised how much protein and fats you can eat if you limit the carbs to a bare minimum and still build lean tissue while losing bodyfat.
3) If I wanna have like a RFD/speed/explosive lower body workout day of sprints AND weight training, do I sprint AFTER or BEFORE the weight room?
Sprint BEFORE.
4) I've constantly been hearing conflicting information about core/mid-section strength in relation to athleticism/vertical jump. Can strength training your abs/obliques/lower back really increase your athleticism/vertical?
Not to the degree that its hyped by a lot of "trainers", and even then its an indirect correlation. The core strength can help you maintain good athletic positions on the field/court and in the weight room by enabling better pelvic control and core stability, which will help, but doing med ball twists and planks wont give you 5 inches on your jumps by itself.
Thanks in advance.