I *think* I'm using IE10 on my W8 machine. Which means I have a Surface type version and a proper grown-up version under the desktop. I believe MS are trying to move away from both Flash and Silverlight which may be why you're getting those messages. I seem to remember getting a prompt about Flash install which I asked it to go ahead and install, since then it's been fine.
I was thinking of installing FF and/or Chrome but tbh there are only about 5-6 sites that get my tabs so I don't see a lot of point in adding yet more registry entries.
My own debate at the moment is whether to replace my soon-to-end HTC/Android contract with a W8 phone or stay with Android or (heaven forbid) join the loser queues around Apple Stores. Omnisphere has a free iPhone controller for the synth but I'd probably only use it once to see if it worked. Had a play with the Nokia W8 phone today but found it confusing, but it would sync nicely with my home setup. So many choices...