New to swimming

I'm new to swimming and have several questions about avoiding injuries. Background: I used to be a runner a long long time ago. Took it seriously, used to train 70 miles / week, ran a 9:32 two mile in high school. But that was almost 30 years ago. Injuries kept me from running seriously any more and used biking as a substitute, and also did 4 years free weight training until I strained my shoulder. Have tried several times to take up swimming and finally this year have been more successful. Been swimming every other day for the past 5 months, would like to swim more but it bothers my shoulder if I go too often. I only swim freestyle, since I never learned the other strokes. So I am basically a very one dimensional swimmer. Watch videos on youtube to try to learn and to actually use a good freestyle technique. I have a 'distance' mindset. Don't like swimming sets or intervals so I warmup and then swim non-stop. Been slowly increasing distance / speed. For October I averaged 1500 - 1600 yards per workout. My average pace now is just under 50 seconds per 50 yards. I've got my 1650 yard time down to 26:58. Long story short, I'm really enjoying the swimming, would like to increase distance and my next goal is to get down to 45 second laps over a mile. BUT most importantly I want to make sure I don't get injuries so I can keep it going. I stretch as much as possible, but I am starting to get some aches and pains in the elbows and also the right shoulder. I think this is related to trying to keep my elbows high.... also I haven't learned to breath bilaterally yet, so I always breath to my left and feel that my right arm goes much deeper each stroke as I turn to the left to breath. I try to keep things as even and symmetrical as possible, but since I always breath left.... My gym has a masters club and I'm sure I'd get lots of good pointers from them, but I haven't joined yet because I don't swim all four strokes and feel pretty sure I won't even try butterfly, and plus they swim 2500 - 3000 yards which I'm not up to yet. Questions: 1. Does the high elbow position, or can the high elbow position cause elbow pain (I have slight discomfort over the medial epicondyle)? Or is that a sign that my stroke is off? 2. Been icing down my shoulder after each swim (elbows too for that matter) and it seems to help but can that mask a more serious problem? 3. Would swimming multiple sets rather than one single distance ease stress on shoulder or elbow joints since you get a breather every so often? 4. Would swimming sets help me improve form? I feel that my stroke is OK for up to 500 yards then starts breaking down and getting sloppy as I get tired (definitely splashing more). Would a little breather between sets allow me to keep better form over a longer time / distance? Finally, I realize it might be hard to answer these questions without knowing how good/bad my technique is, but thought this might be a good place to learn a bit. Thanks in advance for any comments.