I don't believe the issues you are seeing are actually due to Win 8. For instance, Win 8 does not "fudge" your documents (at least it doesn't do it to mine). I think perhaps you need to change the default file format in Word on your computer so that it doesn't save the documents in the newer format. I use documents on my Win 8 computers that were created on MS Word from Office 2003 and they don't get "fudged" by Win 8. The default for Office 2007 and above is to save as a .docx file but you can change the default in Options or you can change it when you Save it by using "Save As" instead of Save which will allow you to choose which file format to save in.
Installing programs on Win 8 works exactly the same as it did in Win 7, Vista, XP, Win 2000, etc... I personally haven't encountered any programs that work in Win 7 but not Win 8 but I'm sure they exist. All of the programs I use have installed easily on Win 8 without any special handling.
The major difference in Win 8 is the Start screen and Metro apps. If you don't like the Start screen, don't use it! I personally don't download or use apps from the Win 8 app store, I stick with regular Windows programs and run them from the desktop. I only see the Start screen once, when I boot the machine. From there it is one-click to get to the desktop where I can do everything I need to do. I don't use any 3rd party apps to make Win 8 "look" like Win 7.
If you use the Win 7 install disks you bought for your old laptop and are successful at installing Win 7 using them, you may have trouble activating that copy of Windows since it has already been installed on a previous machine.
I think you need to find a knowledgeable friend that could help you downgrade your laptop or you need to take it to a shop and have it done. It's not a particularly difficult task but may be beyond your skill level.