1. I'm pretty sure you can region free gc backups, but I load through usb so I'm not 100% on that.
2. 4.2 is fully customizable with 0 drawbacks - I run it myself. It's not suggested to upgrade to if a console was previously modded, but this isn't the case for you assuming you're on 4.2 (do check first).
3. Exactly. Read first, ask second, mod third. The highest brick percentages come from people who skip sections and start assuming. Never uninstall any ios under 200 and, should go without saying, never uninstall or install without knowing what effect it may have and why.
4. Just check out the 4.2 link in my sig below to get started (but again, check your firmware first - Wii options > Settings > top right hand corner).
**Note - depending on how new your console was before you bought it, it may have a D3-2 mobo chip which prevents it from reading and accessing backup dvd media. If this is the case you'll need to load through usb.
And since this was your first post, The Rules at Wiihacks. Welcome and enjoy your stay.