Just fell in love with airliners and decided to get MFS24. What's the right way to learn?

Recently I randomly fell in love with airliners and aviation and have been on a learning spree this past month. Ordered some 1/500 models. Watching every plane related movie and show. Been looking at airline tickets based off trying to fly on certain planes like the 757 lol. My ig fyp is all airline spotting now.

Just bought microsoft flight sim the other day along with a Thrustmaster HOTA. The mfs24 branded one. Basically set controls to easy and have been doing all the training flights and playing around in free flight. I feel like I want to go into career mode and casually fly airliners. Wish there was way more training stuff available.

I would imagine there are some good youtubers out here who have great beginner guides anyone could recommend?

How do I get access to others planes then just the base ones? Would love to fly a 757 or 321neo xlr.

On the tablets which show the flight plan? I see it shows the heading and time it should take to fly to next heading but where do I see the altitude I am supposed to be at? seems like the only way to get that is from the ATC?

Bottom line I am overwhelmed with how to go about things and have the most fun. Thanks for your time!