Yes.
HELL NO. Your files must always remain in sRGB.
Semi-gloss. Sometimes also called Lustre.
Oh, this is SO regrettable
If you use this lab, and are successful in calibrating your screen to match their prints, you need to accept that your online photos will look too blue to everyone else. This is not the greatest tragedy in the world, but it's not ideal.
Soft-proofing can only be done AFTER you are successfully calibrated. You must ignore this part for now.