First you can actually install both on the same computer, so you dont have to worry.
Second you have to log into MySteinberg and follow the route through to the forum, filling in the correct bits as you go, then you can post.
64-bit is better, as it allows you to make use of that full 16Gb of RAM. However, not all software supports 64-bit yet. Check with the manufacturers of your plugins and hardware drivers and see if they have 64-bit versions available. If not, there are ways to bridge 32-bit plugins into a 64-bit host, but how stable this is depends on the plugin. People get best results using Jbridge.
It would play but obviously any 64 bit only plugins wont work on the 32 bit version.
Hardware is subject to the drivers so if 64bit drivers are available then it will work on a 64 bit OS