for everyday boarding - burton custom of your choice
I don't think I would have suggested a Burton Custom for an improver with 3 weeks boarding experience...although I don't keep up with boards anymore so maybe they are no longer suitable for people with a fair amount of experience.
I've currently got a 4 year old Rome Anthem which I like...hence the reason I don't keep up with new boards anymore.
I wouldn't worry too much about going over rocks...get better at picking your path (look further ahead instead of directly in front of you), and practice little hops on flats to avoid rocks etc. Besides, like new phones every shiney new board eventually gets a ding which makes the owner relax and not worry about scratching it. Also, scratches from skis in lift queues are worse than rocks!
With your weight and feet you don't want to go too short...a bit shorter than 160 I think, but look at the guides for your board of choice. As an improver you probably don't want a long freeride board as it'll be stiff and harder to turn. Rentals tend to be freestyle boards as they're soft and springy and easy to turn, so on a freeride board you might find your suddenly rubbish.
You might have to get a wide board...I think Salomon boots come up small (as opposed to Vans), but 11 is pretty big for a standard width board. You might be able to get spacers, but I've never used them so not sure how successful these are.
If you tend to go fast on piste you don't want a pure freestyle board (although that'll be easier to turn), as it'll wobble a bit at speed. An all mountain board leaning towards freeride (such as the Anthem) would probably be a good choice, possibly around 158ish.
If you prefer to pootle on piste, and like to 'bugger about' (i.e. practice little jumps etc) then you might choose an all mountain board that leans to freestyle.
Me...I like to bugger about, but I also like the odd burst of speed. Plus my boarding buddies are fast, so I need a board that would keep up. The Anthem suits me fine.