a) That's a subjective decision, and only you can answer it. It's certainly worth exploring Linux, provided your first experience of it isn't gained on your primary computer - it's the ideal second-computer O/S, at least until you have familiarised yourself with it.
b)No - not unduly so.
c)Earlier this year IBM announced that they were working with Microsoft to produce a Linux version of MS Office, but that was promptly denied by Microsoft. Sun systems make Star Office 7 which is touted as the world's leading Linux-friendly Office suite, and of course there's Open Office, which runs in Linux. Otherwise there's the Code Weavers emulator - called Crossover Office - which has been available for some time.
click here This allows you to run Microsoft Office from within Linux by emulation.
d) There are lots of games which will run in Linux, but developers write primarily for the Windows platform because that's the big market.
click here for pleanty of information about Linux games.
e) No. The OEM licence is for the machine on which the software was first installed, and isn't transferable - it dies when that specific machine dies.