Trying to see what other tires i can put on this and also if i can fit an 11/12 spd cassette & shifters on it? For tires I want mostly something big for the mountains (paved with loose rocks/gravel from rain & firetrails/trails) and sand for near the beaches, and also for snow when it’s winter.

Yes, you can fit new 27.5 tyres and you can fit an 11 speed cassette. 12 speed is a no-go.

Unless you need more gears, or the ratios on the bike are too hard for your riding, I wouldn’t change them.

For tyres you’ve just described varied terrain and weather conditions. Maxxis tyres are a good recommendation, but you may need a few sets to get the most out of the bike.

My recommendation would be to speak with a local bike store, get a few sets of high quality tyres (but them when you need them). They will be a better investment $ for $ over gears. And if you find yourself with some change, get some comfy grips, decent pedals, and a nice saddle (these are known as contact points). Again $ for $ they transform and make a bike more enjoyable than anything else.