I've lived in a rainforest for more than 20 years and run saws for at least 5 hours a week except during late summer (fire danger). Stihl is easily the most popular brand used in the timber industry, followed by Husqvarna. Like others have said, 2 saws are necessary, and the best combo for general use is a 16" bar on a 40+ cc powerhead and a 20" with 55+ cc. Not just because of the difference in weight, but also because you'll eventually get a saw hung up and need another to cut it loose.
Premix fuel is a waste of money, plus Power Punch brand 2 stroke oil makes my saws run cleaner than any premix. Ethanol free gas, called clear gas around here, is essential for small motors with any plastic parts.
Match up the file diameter with the teeth. The chain package will tell you what size file to use. It takes practice to get the angle right when sharpening by hand. A file guide makes it a lot easier, but I only sharpen with a file as a last resort. I have a bench mounted sharpener that works well, but what I end up using more than anything else is this $30 12V sharpener made by Oregon:
https://www.amazon.com/gp/product/B073GSGNLV/ref=ppx_yo_dt_b_asin_title_o03_s00?ie=UTF8&psc=1
I wear chainsaw chaps and steel toe boots if I'm doing any real work. I never run a saw without hearing protection. One of my logger friends is always saying "I'm deaf in one ear and can't hear out the other."