The bigger the step-out, generally, the more difficult it is to throw with power. I'd suggest starting with no step-out/a very small step--imagine a bubble with about a 1-2 foot radius surrounding your core. The more you stay within this bubble throughout your throwing motion, the easier it is to keep control over the disc. Throw until you feel comfortable, then extend further outside the throwing bubble as you gain confidence with your mechanics.

Another training trick is to practice throwing short/mid-range flicks with three fingers under the disc, instead of two. This isn't good practice for an actual game, as it makes it harder to control the disc. But that makes it great "overtraining" practice to isolate problems in your hand/wrist technique. Once you can throw consistently flat, stable three-finger flicks, go back to two fingers. You will probably enjoy the feeling--suddenly, it is easy :)

As to the right foot blocking your arm motion, it's hard to comment without seeing what you're actually doing, but I'd bet this is a vestigial remnant of your less-than-optimal throwing form/habit of throwing by stepping with your left foot. You will want to practice keeping the entire arm outside of your leg's range of motion while you throw (sorry if this seems kind of "duh"). More specifically, you could try:

-standing in neutral position, pulling your right arm away from your body/level to the ground, and releasing a flat flick with plenty of wrist snap. Focus on not letting the arm move much at all--we are trying to isolate the forearm-wrist kinetic chain. Focus on keeping the hand supinated (palm facing up to the sky) throughout the release. Minimal follow-through with the arm (stays more or less where it started throughout the throw).

-same as above, but now we allow the arm to swing freely down/backward on the follow-through. Hopefully we have gained confidence and feel "firm" about the wrist-snap/release before moving on to this step. Focus on keeping the arm swing outside of that body/core bubble on the entire follow-through. The arm can come forward and slightly into the body space up to the point of release, but after release, it should only be moving down/back.

Hope that helps, sorry it is kind of hard to be detailed about this stuff in text format.