Congratulations, you fixed your bike with the help of this forum.
Now you know the right nut why not try the oil change? taking care not to overfill. Between here and you tube theres a guide to pretty much anything you might want to try.
Build it up one job at a time, search here and watch a vid first, come back with greasy fingers to check why its not working out like you thought it would, figure it out and fix it. Its a great and madly satisfying journey in itself, and I'm only a couple of jobs ahead of you on it, working through the 15k service schedule.
A chain and sprocket change a couple of weeks ago would have been beyond me last year. But with the help of this forum I knew to wedge a fencepost in the back wheel and have an impact driver, breaker bar and scaffold pole at the ready, as well as my firstborn son stood on the bike holding the brakes. It wouldn't have worked without any one of those, and still took 4 hrs for what must be less than an hours work for the experienced. But every time I look at that chain I smile, and am enjoying the extra gearing of the suggested 43 tooth rear. No bike shop i know can offer that level of service.
The other bonus is the increased confidence that if something breaks down on the road I may know where to start looking to fix it.