Good deal, Rich! You'll get it.
Stick to 5lb jumps. You're still nailing down the technique, which takes work in and of itself. If you were to jump 10-20lbs because you can (well, you can), you'll get yourself into survival mode and your form will go to shit. Stronger? Sure. Setting yourself up for failure further down the road? Likely.
Those weights aren't going anywhere. You'll get to them soon enough, with better form.
Exhaling at the top? It happens, especially once it's truly a limit set. The key is to remember to get the breath back in, reset the vasalva to protect your back, and to set it back down with proper form. But don't make a habit of doing it during your warmups, as those will carry over to your work sets.
At the bottom between reps, take one big breath, lock that vasalva, and pull. The extra breaths are not going to give you anything; if anything, the extra breaths takes a rep away from you, as your brain starts to think about how heavy it is and the rest of your body is using energy needed to get that last rep off the floor and up to lockout. Easier said than done, but something to work on.
Keep at it!