A few thoughts
My first choice for you considering your needs including financial is the Rossignol Trick Stick. It is their park board, but also their rental board (but with different graphics). I really like how soft it is, but i also really like the camber on it. I will try not to overwhelm you here. I think either normal camber (when set on the ground the center will be off the floor), or reverse camber (the tip and tail off the ground aka rocker, banana) is not the best for beginners, i am really liking what i call hybrid camber, basically it has elements of both kinds.
Really whatever you find a great deal on as long as it is soft. Please dont let a salesman talk you out of this. It will not hold you back as you progress either. Park boards (which are very soft) often make great beginner boards.
If i am not mistaken the boots you have, the prions are a very stiff boot, and might make you feel a bit wobbly. I recommend soft gear for beginners, and everyone actually not going big enough/fast enough to be risking ankle injury (stiff boots help prevent ankle injury). It might be a good idea to try and trade them, or hold on to them for later. When we start snowboarding we are mostly developing fine motor skills in our ankles, and these are easier to feel with a soft boot. Not that you wont be successful in your prions (they are a great boot), just if you had the opportunity to use a softer boot it might be to your advantage