Hi and welcome to the addiction ant this forum
Not being able to extend the elbow sucks but i can't do that either having naturally limited motion range. I wouldn't rush to a doctor just yet for a cleaning surgery (that did wonders for my ankle two weeks ago motion range wise).
The reason the discs rotates clockwise in the air is heave off axis torque. Meaning something forces the disc to rotate just as it is leaving the hand. OAT is the abbreviation and it's a FAQ often described here. Wrist rolling, arm dropping low in the follow through and unclean releases from the grip disc bottom scraping or sticking to the fingers. The hip and shoulder bones might be on unequal heights from the ground and that would tilt the disc sometimes in unintended manner. You might wanna check the technique repair section on the main page too.
The flipping is made worse by your varying final step landing position. The right leg lands left and right of the line you x stepped on. Landing left of the running direction tilts the body right or clockwise tilting the disc the same and it is the correct way to throw anhyzers and rollers. At times you put the right leg on the ground to the right of the line for a hyzer tilt and lo and behold on the second throw the disc flew on a hyzer so you already have that shot.
The place you start at and end up on in the tee and the place where the follow through step lands matter also for avoiding OAT. Annies start from rear right and depending on angle end up in the middle or the left of the front of the tee. Reverse for hyzer and straight down the middle for flat shots. The follow through landing step position should be a mirror of the plant step. Which is the final step of the right leg before the disc leaves the hand.
You don't reach back far at all and that is the major limiting factor to your backhand distance now. BTW. you have good forehand distance which sets the bar high for backhand so don't worry
The reason you can't reach back ain't your physique it is because you don't point the feet and head 180 degrees away from the target. That allows you to almost double the arm stroke length. Since you are athletic and have experience of using your body balance shouldn't be an issue. Just make sure you always step each step without being flat footed to not twist the ankles, knees etc. Reaching back fully will be way different feeling and awkward and most feel they'll fall down and thus won't throw at all and lose distance at first. It is natural and can take months to get over. With your background i hope that your learning curve is shorter.
Check out Youtube channel mfranssila for throwing technique differences between yourself and some elite throwers. Especially the dual angle slow motion video of Avery Jenkins. There's also channel lcgm8 where there's a video 7 throws with Avery Jenkins and many other comparison slow mos in various vids such as Tali Open 2009.
Notice how you did not twist the hips to the right of resting position at all? That is the second largest source of power. The second major loss is lifting the left leg off of the ground before the disc leaves. You should not kick the left buttock with the left leg. At this rate you take a lot of power off of the arm motion forward. Sir Isaac Newton wrote something to the effect each motion has an equal and opposite force. That means that standing on one leg and throwing will put half of the power into turning your body to the left. No joy aiming and power generation wise. To rectify that you should either keep the left leg on the ground (see Avery for toe only on the ground to see how flexibility concerns are alleviated by the left foot being vertical at the rip) or doing what Dave Feldberg does to counter the arm swing counter force by kicking the left leg to the right and well forward.
Here's a great tip to help in not having the arm drop low in the follow through like you did: Right after the disc has left rotating the thumb to point down allows more freedom of movement for the shoulder blade which can stop the rising follow through motion for hyzers. If a flat shot arm swing drops below horizontal in the follow through that is a recipe for flipping discs and rollers.
All of these things are repeated in video critiques so if i were you i'd look at many of them for tips too. Have you seen this? : http://www.youtube.com/watch?v=nED7gcXobEo
Flat shots need running on the center line of the tee and planting each step on the center line. Anhyzer needs running from rear right to front left with the plant step hitting the ground to the left of the line you're running on. Hyzer is the mirror of that.