Noob's Macbook Pro 8,2 and Sequoia questions

Hello,

before anything else - please bear with me :)

Couple weeks ago while scrolling through local auction site I stumbled upon a Macbook Pro 15" from early 2011. It was being sold as "working, but with defect". The defect was the bulged battery that also cracked the touchpad, so it was being sold without drive, battery and charger. For about $15. Bargain in my book.
And since I've never used any Macbook in my life I thought it might be a good opportunity to tinker with it and just learn about MacOS in general.

So I've installed a 512GB SSD, replaced that broken touchpad, added new (replacement) battery and a charger and I've installed High Sierra on it, since it was the latest, officially supported OS this machine should be able to have. I'm also planning on putting additional 8GB of RAM, since it has a single 8GB stick and I've read that despite supporting only 8GB total, it should work with 16GB.

But since many apps from the store refuse to install on this machine, I was wondering if I could install OCLP and force an upgrade on this thing. But that rose some questions:

1. Is it fine to force Sequoia on this machine?
   
2. How cumbersome is it? (I've spent about 2-3 hours looking up a way to install High Sierra on this thing with some terminal commands and network recovery thingy, since the servers were supposed to be down... but they weren't)
   
3. Even if the upgrade goes smoothly, OCLP does some post install stuff. If I were to reset the machine to the factory settings to, let's say resell it (with Sequoia installed) would it still work fine?

Excuse my long post - this is MacOS, and Apple environment noob speaking here :)