The haitian anemone is the most easy to care for in my experience and they are usually cheap 5-10 dollars so you can try one and see how it does without a big wack to the pocked book.
Nems need a mature tank (9-12 months at least) and good lighting, bubble tips are one or the easier to keep but still not recommended for beginners.
If it's for clowns they will also (maybe) host other things from powerheads and leather toadstools to caves and filter intakes.
If it's for that 'nem' look torch and frogspawn corals look much like nems and are easier to care for.
Research buddy, what I do is read about something untill I don't want it anymore, then if you see one and you think 'hey I am gonna buy that!' you know the lowdown
Not certain mate, I don't intend to keep nems for a while but I really like BTA's.
Sand nems need a sand bed of at least 10cm i think and needs moderate lighting and plenty of water.
My LFS has a BTA in a 200lt tank and it looks great but either way you still need a mature system.
Hopfully one of the guru's will be along to offer more insight.
What sorgan stated is correct.
All nems need a good sized tank, a mature tank and higher end lighting. Also take into consideration that in reef tanks, nems can sting and kill corals if they can reach them.