there’s a reason tiffs aren’t used online... they tend to be large files. given that the web is @ 72 dpi anything uploaded is going to get downsized anyway. i use tiffs for print pieces but prefer jpegs, pngs or pdfs for online.
if you have photoshop, you can batch convert files pretty easily.
Not at all, just open the tiff in the program and save it as whatever format you choose. If high quality is your aim, formats such as JPEG are not lossless, and will result in some slight degradation, but for purposes such as posting online it's fine.