I hear a light (think heather) gray tee underneath won't show through a button down. I've never tried it myself, but I've heard it works. If not, just get a thicker shirt (oxford cloth) and wear an undershirt anyway. There's no harm in wanting to be hygenic.
rub some aloe on it and avoid the sun for a long time. The little bumps are your body's way of letting you know you should avoid the sun (your skin is blistering).
just be careful, there are some dangerous people out there. I've heard of success stories and horror stories, and it's hard to know what you're in for. Just remember that the internet comes with great annonymity and some people abuse it.