Refurbishing MacBook Pro 2012

This laptop has served me well for over 5 years and is still going strong. Thank you, Apple, for building a quality product.

There are three areas I may need upgrades.

I tend to keep many Chrome tabs open and that eats up much of the 8 GB memory. When I originally partitioned the disk, I didn’t allocate enough to Windows and am left with about 8 G available. I keep it mostly plugged in and the battery lasts about 2 hours on its own. So,

1- How do I upgrade it from 8GB to 12 or 16?

2- Should I replace the old 250GB SSD with a larger one or can I do non-destructive re-allocation between OSX and Windows?

3- How do I check my battery health and if needed, which aftermarket battery should I replace it with?

Thank you.