If you dont care about saving any info on your disk just reformat and reinstall.

Make sure you have all the drivers for your hardware before formatting, especially you network drivers.
Back up your user folder,and any other files you sent to some other places on your hard drive.
Make sure you have all the license files for your software written down (Microsoft Office, Games, other programs).
If you have the room on an external drive, I'd image the whole drive (just in case something does not work or you forgot to backup something).
Once all of that is completed, format that thing.
After a month or so, and you find all is good and your not missing anything, delete the image file.
Don't forget to create an image of your new install, for any future problems you may encounter. Too make it a smaller file, do it before you load all your games.

you can install an external Start button even for w 8.1

If you´re installing the OS in an SSD, it is said those drives have better performance if you use AHCI protocol in the motherboard instead of SATA (you should be able to change that in the motherboard bios).
Also, remember SSDs are fast enough that you don´t need drive indexing, try turning that off as soon as you finish installing the OS. Then turn off Super Fetch (a file list which function is to try to order the execution of files in a way that results in faster desktop load), again SSDs don´t need that, it was thought for HDDs.
And lastly but not least importatnt turn off Defragmentation in the SSD drive (don´t forget about it), SSDs are usually TRIM enabled and W7 is TRIM capable so the SSD should automatically recover lost space and won´t fragment itself, besides Defragmentation is bad for SSD, since it shortens its lifespan if subjected to defragmentation.
Sometimes the OS fails to detect the SSD and do this for yourself so it doesn´t hurt to check they are off.

Win 8 is the new Win Vista (yes yes I know it's fixed after the update. Shut up)

Win 7 is the new Win XP

Now I don't want to know the new Win ME.

windows 8 new ways of spying on you ^^

Don't forget your chipset / motherboard drivers! Actually, it's a good idea to do those first before any other drivers.

One tool you can use for drivers is SlimDrivers: https://www.slimwareutilities.com/slimdrivers.php

Ughh, I forgot:

The one thing I would definitely need is my Thunderbird for checking eMails. I don't want to set it up again, do you know if there is a "backup" or rather settings and password export function?

...that I don't have it. ;)

.......That now more people are using linux.

You'd want the entire %USERPROFILE% folder just to be sure since games save in various locations within there.

If you use Steam you'll also want its steamapps and userdata folders from Program Files, or wherever Steam is installed to, since most games don't use Steam Cloud; if Steam isn't installed on the drive/partition you're wiping you can just leave it where it is and install the new version over top of it to make it see your existing data. Thunderbird data is stored in %APPDATA%\Mozilla. Firefox is also stored here if you use that. Restore the folder to the same location on the new install and it will seamlessly continue with the existing data.

No, 8 was never like Vista. Vista was a memory hog, didn't deliver promised features and had huge compatibility issues with existing machines. Win 8's problem is 80% people resistant to change. Win 8 actually restored old compatibility 7 took out like VB6 compatibility, is less memory intensive than Win 7 and starts up much faster.

Good thing PC users don't use Macs. They would riot in the streets by comparison with Apple's constant wholesale changes in hardware compatibility.

Are you sure about that? They look like the same price where I'm looking, and I still don't feel over the sticker shock.

Vista made you turn off a main feature (UAC) in order to actually work on the machine. And like you said it was way too bloated, it was a major disaster.

Windows 8 has an awesome task manager, ability to reset (instead of having to reinstall), IE 10 (backported to 7 - wise decision)

The only valid complaint seems to be that the start menu is missing. Download and install Start Menu X and enjoy the rest of the system... I don't understand what else is so wrong with Win8?

And for OS X, yeah they're aggressive. That has its positive side though, it keeps users and app developers on the leading edge. Legacy code has its place (this site is a prime example) but Apple has evidently taken the stance that legacy machines can run the legacy code. Microsoft still has the "one machine/install must do everything" viewpoint. You pick your poison I guess.