I suggest you look into buying some last-season boards from the big names in snowboarding (Burton, Rome, Never Summer, K2, etc). You can get stuff for half off. Do some research on what you want to do, and don't just buy a random package on ebay.
In terms of sizing, 163 is more your size than 161, but it wont make a huge difference.
If you just want to get into riding in general let me suggest a few wide boards for you such as the K2 Select Wide, Atomic Exeter, Burton Royale, etc.