1. It is not a gaming system, If games is the number one use, look for something with better video.
http://www.anandtech.com/show/7047/the-haswell-ultrabook-review-core-i74500u-tested/7 Your cpu is also shown in these benchmarks. You would need low settings to make most games run better. LoL does not have requirements of the games tested in this link, but gives you an idea of gaming performance.
2. The basic hardware seems to be Windows 8/8.1 ready. Honestly, I do not see a reason to upgrade with 7 being fine for most users.
3. Based upon images from the internet, you would need a bit more work to get to the internal network card(this is IF it is upgradable. That info is not available from what I can see.). The USB stick is simple as plugging in a keyboard