Normally you would need to go to college, I believe a 2 yr course. Normally done as day release from an employer.
Reading drawings is relatively easy, i would say after about 60 mins and ten different drawing, with someone pointing out what is what, is normally enough to read them. Thats how i learned.
There are different standards of welding, to do structural work you really need to be coded
You really need to look at your goal and then see what qualifications you need to attain that. If you want to be welding oil rigs underwater then you'll need a lot more paperwork than if you want to stand on a production line all day glueing golf trolleys together.
Really if it's a career choice then remember that you want to find a job that will put a spring in your step when you leap merrily from your bed in the mornings. Or at the very least, stop you reaching for the razor blades.