learning to snowboard is quite a bit different from learning to longboard. it's a lot more frustrating, though he's more than likely to love it once he learns.
to OP: i'm thinking 155 is a tad too long for what you intend to use it for. i'm about your size (5'7" 135lb) and i ride a 152 that feels a tad too long for the park. i, personally, feel that a 148-150 would be great for me to do all mountain freestyle. i'd recommend going with a 152 for you. it should be stable enough to get you around the mountain, and short enough to transition you into park.
as for waist width, you have no need for a wide board. even midwides aren't necessary. reason for this is boots usually have an incline on the heel and toe, and bindings provide enough lift to get your feet up off the ground to negate what little heel and toe drag you get. i never experience any significant drag even on hard carves with a smaller waist width board.
as for the boots, try them on and do a bunch of range of movement tests to see if there are any pressure points.
for boards i'd recommend looking at Rome, CAPiTA, Battaleon, and maybe LibTech (though i wouldn't recommend rocker as a beginner).
Last edited by kyouness; 11-05-2009 at 12:20 PM.