Like the title says, I don't have any issues right now, just some general questions.

I am newly back to biking, so I am a beginner at bike maintenance. As a teen I rode seriously, but I'm turning 50 this summer so that was some time ago. My previous adult bikes, I simply had the bike shop take care of the bike for me. Well, I didn't ride much (I was quite fat for years, but I'm losing weight, down 75-80 LBS since Sept, so that will change), and it still got expensive. So, when recently buying a new bike, one of my goals is to learn to maintain my own bike. When I got it, I thought the seat was way too high, but instead of having them change it, I did it myself (simple job, and after watching some You Tube videos and reading about saddle height, I now know I need to move it back up a bit, though not as high as when I picked up the bike). On my first ride, I was having issues with shifting, I couldn't get it into the lowest gear for going up hills, but with a few You Tube videos and a little reading, adjusting the derailleur was a snap (there are a few hills around here where I need the lowest gear for part of the hill).

So, for my questions...

First, how much should I do as a beginner? I'm only semi-competent with tools, I'm far from a handyman, but I can do basic maintenance around my rental home, and I changed the oil on my motorcycle once (with the placement of the oil filter, and many scuffed knuckles, I decided after that once that it was worth paying to have it done). After a year or two with my bike (a Giant Escape 2), I'll probably want to start upgrading components. Which ones should be relatively safe for me to do (safe both from an actual safety standpoint, and also from the standpoint of not totally messing it up and making the fix far more expensive than taking it to a bike mechanic for the work to begin with)? I do have a friend (a co-worker) who is also a bike mechanic, but since that is his part-time paid gig, and his former career, I don't want to take too much advantage of him, but I can get my mistakes fixed relatively inexpensively.

Next, what is done in the typical yearly tune up?

Finally, what tools do I need? Right now I have a decent basic tool kit, but anything bicycle specific that I need?