seeding the base rock will work, ive never done it so im just gonna estimate about a 1:2 or 1:3 ratio of lbs of live rock to lbs of base rock.
it will slow it down a bit, but it should be fine.
if i were you i would wait until the tank is cycled, add a smaller CUC (maybe 10 snails and 2 hermit) and then about 2 weeks later add about 10-20 more snails and maybe 2 or 3 more hermits.
then in another 2 weeks add the 2 shrimp.
wait maybe another 2 or 3 weeks, and then i would say it's safe to add a pair of clownfish.
for a tank that size i would recommend either A.occelaris or A.percula (both look like "nemo")
now unfortunately there is no way that you would be able to keep a yellow tang healthy in a tank that size. if you want something else i would suggest a Goby and pistol shrimp pair.
certain species of gobies and pistol shrimp have a symbiosis together where the shrimp makes a burrow while the goby keeps watch. its super kool to watch.
for gobies i'd suggest either a high fin goby, a yashia goby, or a randalls goby. there are also many more different gobies to choose from, so try looking some up in an online store, like J&L for instance.(link below)
http://www.jlaquatics.com/phpstore/s...s/mainpage.php
there are many other ways you could do it, but i like that one so that's the one i suggest.