What is the best kind of taper to buy? I've read that steel is the best and to avoid acrylic
Steel is probably your best bet, as all the acrylic tapers i've seen haven't been as gradual as steel tapers. Since tapers aren't worn as jewelry, I don't see anything wrong with using an acrylic taper as long as it's followed by a plugs made of a suitable material (steel, titanium, glass, etc). But I would recommend steel over acrylic any day.
I've read of people have reactions to O rings are there different materials that is used for O rings (plastic,rubber, etc)
People usually have reactions to the black o-rings made of nitrile, but some people may have a reaction to the clear silicone ones. Most black o-rings are made of nitrile, and most clear are made of silicone. I've never had a reaction to either, but that's me. If you know you have an allergy to a certain material, stay away from it! if you don't want to take the chance, i'd sugest using the clear o-rings. They look better in my opinion, anyway.