Much of my experience is kind of dated, I learned to weld with Acetylene and oxygen.
Caterpillar sent me to school to learn stick and MIG, when my contract was up I moved on. Politics, not the job, the job was great.
Like mentioned, it messes with your lungs, I developed a chit load of allergies over the years, most likely due to inhaling fumes and increasing my sensitivity.
If I had to do it again, I'd include a forced air mask (and particulator/filter) into my kit from the beginning.
I've burnt my eyes on numerous occasions, no matter how good the mask, reflected UV can find it's way in and in production work you repeat positions constantly. You often don't realize you've burnt your eyes till the next morning. I finally found a redundancy for this, I wear UV filtered glasses (wrap around), near clear lens that filters UV as my regular eye wear. They are also balistic ülastic hardened and scratch resistant. Even if you don't need gasses something similar is a good idea, redundancy is smart.
I'm retired now but still have a pickup, generator, gas, MIG and stick setup that I can drive out into the field to repair farm machinery. Spring and fall I keep pretty busy. Sure helps supplement the retirement. Actually more of a blacksmith than a welder, I do a lot of fabrication that doesn't require a micrometer to do. I also keep some sheet metal breaks and other sheet metal tools around.
A lot of ways to go once you have your ticket, I did a lot of work with high pressure gases and liquids.
Take metallurgy along with the welding coarse, they offer some with the welding coarse. But supplement it with some serious study, it opens up all kinds of doors that a regular welder might not be able to access. Be a complete welder. Good math skills are also a must. Drafting, isometric drawing and CAD are also helpful. Now on days you almost have to have advanced computer skills, to setup the welders in manufacturing.
