Yes.
When iTunes is upgraded, it preserves your music library so just run the upgrade process and you'll be fine
No
yes
Quicken can upgrade to QuickBooks, as they're both made by Intuit. The upgrade should be seamless.
You can't. You have to pay or risk losing your account.
No. If you are downloading your computer needs to be on
If think that this doesn't work because I've tried it before
Yes. Just click "buy" and drag the song over to your playlist.
It is possible if you check off the syncing, and choose manual upload.
You can't. If you sync with iTunes on another computer iTunes will force you to wipe the iPod.
Yes you can, but you will have to redo the jailbreak process. When you update your iPhone is it wiped clean and reinstalls the new OS from factory defaults. This is also why it is so important to backup your data prior and why iTunes does it automatically. Back up your iPhone before you update it. Then jailbreak it and then restore it with the previously backed up content.