Dual Boot... YES PLEASE!!!

I'll answer what I can.

1) The Ubuntu partition will be able to read the Windows partition, but not the other way around (or at least I haven't gotten it to).
2) Pretty safe. Worst case scenario it will have to do a start-up repair, but thats no biggie.
3) You will have to use Ubuntu's Grub, and I'm not sure if it will let you set a default or not. Worst case scenario, you will have to choose every time.
4) It's not always the easiest to do but others on here have. Use the search function.
5) Nothing off the top of my head. I use it because I can boot from my external hard drive or the cd in case I can't boot into Windows for some reason.
6) They are a lot harder to get with Linux (because there are fewer of them), but if you can find a decent Linux AV, it might be worth installing.

ad1) I assume you want to access common data. Why don't you set up a seperate Data Partition. I am not an Ubuntu expert, but I think it can deal with NTFS.

ad2) It is safe. I never had a problem.

ad3) If you have 2 seperate HDDs, I suggest you install Ubuntu on a disk seperate from Win7 by disconnecting the Win7 OS disk. That way you do not get into this double boot mess with the MBR and you can prioritize the boot sequence in the BIOS.

ad4) if you make the setup as suggested in ad3, you just delete the Ubuntu partition. If you do a true double boot, you have to mess around rebuiding the MBR for Windows. MBR - Restore Windows 7 Master Boot Record
A completely different approach would be to run Ubuntu in a virtual partition. I have done that with Virtual Box. This is quite simple and whenever you want to get rid of Ububtu, you only have to delete a couple of files.

ad5&6) I tried Ubuntu for the learning effect. It is quite different to Windows and a little hard to learn at first. It is a lot less subjected to malware (because of the small user base it is not an interesting target). But I don't think it gives you more function than Windows - at least I could not find any.

Edit: Hmm, I guess Petey7 was saying the same thing 1 minute ahead of me.

Virtual machine or virtual partition = same thing.

EasyBCD can read both Windows and Ubuntu...
I like it better than Grub.