As far as shrimp go, you can have whatever kind you want. I personally like variety. Fire shrimp are the brightest but hide a lot, Cleaner shrimp will help eat parasites off your fish, Sexy shrimp add life to your tank especially in small groups, same with pepperment shrimp. ITs totally up to you.
What are you wanting the snails for? Nasarius snails do good in the sand. Astrea snails help keep glass clean, Mexican Turbos are great algea eaters but can knock your corals down and also can not upright themself if they fall.