I'll skip the overhand slide, but here are your other answers:
For playing with a slide you need your action (string height) high and heavy strings. I manage pretty well with .10's, but for a really mean sound, I would recomend even heavier. Anyway, there should be a mid-point, where you can use your guitar for slide and regular playing, but it's a compromise. So, if you have more than one guitar, I recomend designating one of them for slide.
Try it with regular tuning (EADGHe, but also with open E (EHEG#He) or open A (EAEAC#e) - just tune the strings to the pitches of a chord shape.
Set your gain as low as your ego can take, at least for the beggining, and later experiment with all the effects you can get (for ideas reffer to a few Pink Floyd songs, there's some slide on every album).
Don't get a cheap steel slide because it corodes quickly.