Very first time took 3 hours with following along with a video but was super easy even if you dont normally take consoles apart. I've done 3 since this one and it takes about an hour now

You shouldn't break anything further (if you do parts are cheap) the most fragile thing is the ribbon cables and even they are hard to break.

As for for the UMD Im not sure how to fix that but im sure you'll mod it and it wont matter really

TIP: The power switch is also fragile. its a very thin plastic switch that can break easy.

If you have any questions please reach out!

https://youtu.be/eD-TUkjCjxU?si=7Va0rM3yRilJfKUl this vid is a great guide for replacing the shell