There are three species of shrimp commonly sold. Like fish they won't tolerate any amount of ammonia or nitrite, and copper (in medication or fertiliser) will kill them stone dead.
Caridina japonica (Caridina multidentata) Amano Shrimp Gets to about 2" for a female, 1.5" for a male Will not breed in aquariums, the larval stage requires salt water. Temp 68-82?F/20-28?C pH 6.5-7.8 Transparent Grey-Green, with brownish spots forming broken lines and a white stripe down its back.
Neocaridina heteropoda Red Cherry Shrimp, Yellow Shrimp Gets to 0.8-1.5" Temp: 62-82?F/17-28?C pH 6-8 Breeds very readily (when I moved my shrimp into a larger tank I found I had well over 100 juveniles of them from two pregnant females. Larvae are smaller versions of the parents. Mine seem to happily tolerate London water with a hardness of about 15 degrees.
Caridina cantonensis Bee Shrimp, Crystal Red Shrimp, Tiger Shrimp, Black Tiger Shrimp... Lots of varieties some very expensive indeed. Gets to 1-1.2" Temp: 64-78?F/18-26?C pH 6.5-7.5 Lots of different varieties, and again breeds readily in freshwater like N. heteropoda. Being the same species these varieties will happily interbreed, so should be kept separately. It won't breed with N. heteropoda though. Prefers much softer water gH 4-6, kH 1-2 than the others will tolerate (I've not tried any yet for that reason). Some varieties are very inbred and even more sensitive to variation. While the wild-type "Tiger Shrimp" might cope a little outside this range, the high grade Red Crystals or the Black Tiger certainly wouldn't.
All shrimp will happily eat hair algae and the various micro-organisms living in it, with regular supplements of algae wafers, flake, bloodworm, shrimp pellets or blanched vegetables- they'll happily scavenge on what your fish don't eat, but if you keep them alone, they'll starve if you don't feed them.
They should be fine with snails (I've seen mine happily picking algae off the backs of them), but I'm afraid I don't know anything about Bristlenose Plecs. As a rule if it can fit the shrimp in its mouth it'll probably try eating it. Even if it can't it might well pester them to death nipping at it.