i bought a snowboard before i had ever even been to a mountain, let alone learnt how to ride on one!
i didn't fuck it up, in fact it lasted many seasons.
your friend may not know what detuning is... but so what?
he can send it to the shop for what ever tuning.... he can read a book or a www page like this and find out all he needs.
i don't understand why you would care what your friend does, as long as you can go ride together then just be glad for having friends who enjoy the same stuff as you. altho to be honest, i reckon you are just jealous and that you would want to be able to splash the cash on a board of your choice.
this certainly ain't anything to get pissed off about.
but i would agree that if you can only buy one or the other between board or boots, i would get the boots first. every time.
and as for lending your board to him. well if you don't want to, then don't. your board is like your bird... you get to ride her and ONLY YOU.