It sounds like all will be fine but where are you getting the idea that you cannot go up to certain lengths because of your height? If you chose not to buy a certain length of board as it “doesnt come up to your chin or nose or whatever” and it meant that you would suffer once riding it over certain conditions due to the extra weight.. would you still go out and buy a board that is supposedly the correct length for your height? I wouldnt.
If you were 5ft tall and 15 stone with size 7 boots, you couldnt ride a board thats a decent width for your feet along with it being,say, 140cm on the likes of groomed snow (wont mention powder here) and expect to tank around the mountain on it. You might be able to slide or spin around on it in a fun park but for all mountain playing about you would have to go up to something that can cope with the weight your placing on it or you could be finding yourself riding at 90% when theres so much more to be had.. if you had the right board.
Ive still got a board from 96 thats too short for tanking about on now that i weight 14 stone. its just not useable and i dont get on with it at all. when i was 11 stone it was amazing.. it was a great all rounder.
Theres other things you could run into as well. I found out that on Cairngorm i couldnt use a certain length of board with whatever sidecut it had as i just couldnt turn it within some of the runs. I could slide it, but never cut a proper turn on it.If you arent going to be limited between snow fences then this wouldnt stand out so maybe it wont be a prob.Just thought i would mention what i stumbled into a while back!
Speak to someone that has boarded where you plan on using it and try and get a shot of some demos as only you will know what feels right. Hopefully folk that have the local area knowledge along with board knowledge will narrow down the search and make it as easy as poss for you.