I’m 5 foot 6 and not the slimmest build.
What size board should I look for?
Board length is less to do with your height and more to do with your weight, although as a very rough guideline a typical ‘twin-tip’ should come up to in-between your chin and nose when holding it in front of you, however:
longer boards* ‘float’ better in softer conditions as your weight is distributed across a larger surface area especially in powder(not hugely important when starting out though …)
Shorter boards* can make it easier to initiate your turns as the side-cut is shorter
*some modern board designs can mitigate these two generalisations to a certain extent.
As others have said having your own boots is nice – soft->medium flex/neutral for beginners.
And +1 for the McNab ‘Go Snowboard’ book.
And lessons … lots of lessons!
Are all snowboard bindings the same?
No … some fit some snowboard boots better than others – it can be a bit of ‘pot luck’, but finding a pair of boots that fit *your* feet is the most important thing when starting out. Most bindings can be adjusted whereas your feet can’t!
Some bindings are for free-style, some for free-ride. Historically the former were soft/medium flex, whilst the latter were medium/stiff