I routinely suspend / resume with no problems, I expect you will be able to as well. Your browser will lose some context if you close it. The Pig UI in particular will save state server-side so even if you do close some things will pick up where you left off, but other UIs are not quite the same way.
We sized the sandbox to very modest hardware profiles and all of our tutorials will function with only 2GB RAM. Certain aspects will be a lot faster if you give it more RAM. In particular the Pig tutorial is quite slow with 2GB RAM due to extensive paging within the guest. If you increase to 3GB there will be little paging and at 4GB no paging at all. The Hive tutorials are pretty quick even at 2GB. If you have the hardware, 3 or more GB will make things go a lot smoother.