For slide playing, you should never underestimate the power of open tunings. What turned me on to slide was a German Rockpalast special in about 1980 where Pete Haycock of the Climax Blues Band explained open tunings and I just thought "So this is how it is done...", I'd never been able to figure it out until then. For starters I would say just tune your guitar to open G (DGDGBD, low to high) or open D (DADF#AD) and try to experiment a bit and sooner or later the familiar blues licks will just fall into place. The G tuning has a somewhat "sweeter" sound but some basic voicings are available on both in different positions.
But I also higly admire players like Rory Gallagher who in the middle of a tune could jump into standard tuning slide effortlessly. What is crucial for standard tuning is damping with your fingers behind the slide to eliminate undesired notes.
As for the material, I think on the acoustic metal definitely works best. Glass gives a somewhat lighter sound on the electric, but you have to press on it somewhat harder. Duane Allman used little medicine bottles. My own preference is copper, cut from a piece of heating tube, which I've been using for as long as I can remember.
Lately, for most acoustic slide work I prefer my Tricone resonator guitar, played overhead like a steel with a Dobro bar. In addition to open G and D I also sometimes use a tuning I picked up from David Lindley, another big favorite of mine. It's almost only firsts and fifths, BF#BF#BD# or a half step up: CGCGCE. You'll need heavy strings for that. It gives kind of an eerie sound, most standard blues licks are not easily available with it.
