I've noticed now my MBP stays in between 65-80 degrees Celsius, I'm wondering if this is cause of the battery in any way, it used to generally be at 45-50 degrees Celsius just chilling?
There is your answer mate. If your not confident opening it up take it to apple or a service centre.
Set up an appointment for Wednesday, will tell them open my baby up but also swap out battery
you think they'd replace my whole bottom portion due to the scratches and it missing the little black things?
They have spare feet generally. And they won't replace the battery unless your paying. Tbh if it's still showing greater than 80% Health then your wasting your money.
I would bet a large sum that your issue is dust bunnies.
That's a different story then. Yes it'll be replaced. I'd recommend checking your cycles before you go.
If your at less than 1000 cycles you could argue and get a free replacement.
Honestly you've done well!!