Apart from frequent images (Acronis) I also have a complete, and frequent, copy, to a safe place, of all the relevant, and possibly changing, folders under "username". (Favourites:My private files: Pictures etc.)
Like most, I have plenty of space, so I always start with a dual boot install. It matters not, to me, whether this is on a created partition or another hard disk. A quick check of the new installation, and I then customise the more common aspects, to my own taste. First thing then is to create another image for future use.
I install all my software. - Not such a big task as yours! I have (just counted), 39 regular third party programs. It takes about 4 dedicated hours to get through. After customising each of these programs.where needed - another image.
I usually run the new installation for a few days before considering anything else. If it is a legacy OS, then it may stay for a long time. I still have Windows 7, for example, in a dual boot, as I refer to it when I visit Windows 7 forums. This will be coming off when, as you surmise, next months release to the public hits the shelves, and the 8 forums pick up.
EasyBCD is a must for me, but, of course, you can remove the dual boot with MsConfig also. Only thing to be careful with, is where exactly your new boot manager is placed. Even this can quickly be sorted with the repair function of the installation DVD.
Even after those precautions, I sometimes overlook something that I needed. I did this, originall, quite a bit with my old Email, but since I learned that lesson, I now have a separate folder, on a safe partition, for my mail.
Your question in the middle of your post! I cannot think of any problems that a dual boot would cause, but, personally, I am cautious of upgrades. I have never been in a position where I needed it, and always do a format and clean install.