In your situation, i wouldn’t change the drivetrain. As you say you’re running a 28t chainring with an 11-42 cassette, which gives you exactly the same easiest gear as a 32t chainring and Sram eagle 10-50 cassette which is how most brand new bikes come. If you want to try something different, perhaps try an oval chainring. I’ve never tried one myself but I’ve heard a lot of people say they help with power transfer and it makes pedalling easier.
My recommendation would definitely be to upgrade the wheelset. Reducing the rotational mass of your bike (wheels and tyres) will make climbing feel so much better. Perhaps have a look at something like Stan’s No Tubes Arch MK3 or Hunt Wheels Trail Wide. Experimenting with different tires is good also.
It looks like your bike already has a dropper post so no need to buy one.
As for suspension tune, watch some videos on YouTube etc and have a play yourself. Another option is ask at your local bike shop to see if you can rent a ‘Shockwiz’ for the day. It’s a device that can help you dial in your suspension settings.