There are few ways, but eventually MS will force you to update. I am currently with 7.41 and dont have messages for update. Depending of you OS you could stop the skype upd service or redirect the update IPs.
Fist you want professional backup solution for free this is the hardest part of your issue. Second if you are using HDD to make you backups ofc this will shorten the lives of your drives there are special HDD for this.
About free solution try Acronis or Comodo, if you want...
Depend of the virus/work your system is infect and it does? True - there are less virus developed for Linux, but people that written them are smart enough. Most virus are designed for specific OS and wont work on multi platform, there could be exception but they are not that many.
No clue what you mean whit that "mobile workstation", you are starting the question "laptop preferably a gaming one" and then going in a different aspect. If you need help make the question more specific so we could give you proper answer.
If you never use Linux this is friendly one here is link for download : http://www.ubuntu.com/desktop/features
this is the other : https://www.debian.org/distrib/
If you dont like it you could always search for some one who is selling key for example Windows 7 xxxx version, just to know Win7...
None OS laptops and PC are preferred from a lot sellers and buyers because the price is low then whit included Windows( most Linux are free and Mac OS wont run on every laptop/PC). If you ask me I never buy laptop or PC whit install/included OS on it the price is high. Installing OS require some...
Why you dont try just too boot live cd/usb OS and repair the advapi32.dll file that would save you the new installation and you can run scan to check is this issue is cause from malware/virus to avoid reinstall OS again.