Hey! To answer your questions:
1: Yes and no. I started with the exact same camera. You can get by with it for a while as a starter camera, but if you want to do it as something more than a little hobby, I would recommend an upgrade to a higher quality camera. The only thing the SX60 has over my current camera is the ability to contrail spot. The toggle zoom can prove to be quite ineffective, especially when up close.
2: I use Lightroom and Photoshop, with the majority of my editing done on Lightroom. Everyone has their own style, so I won’t tell you specifically what I do because it’s worth figuring out what you like on your own. For more standard photography (JetPhotos mostly), I crop the sides, level, sharpen, and reduce noise in Lightroom and an add-on group of apps called Nik Collection (which unfortunately isn’t free anymore). I then add contrast and add or reduce brightness, and crop the verticals down to a correct ratio in Photoshop.
3: No. Optical zoom is the zoom you want. It’s the natural amount of zoom the lens can do. Digital zoom is the quality-reducing one. It takes the fully zoomed-in image, and effectively crops it further, zooming in on the image portrayed in the camera as opposed to the subject itself.
4: Yes. Kind of hard to spot without zoom. Different amounts and styles (crop sensor, wide angle, fisheye, etc) help and hinder different aspects, so if you can afford it, get a couple different kinds of lenses and maybe even multiple bodies, to see what you like and/or to use in different experiences. I only have 2 lenses and one body, so I can’t really speak to the worth of extra bodies or anything, but I am looking at getting a longer lens, hopefully in the near future, to get the quality of my shots up even more.
Keep practicing is the main advice I give anyone. Nothing comes naturally - I’ve been at this for 2.5 years and still have a ways to go. Find your own style and niche and do what you like, and take opportunities to learn along the way. Good luck in the future man! Can’t wait to see your shots :)