This is what I would like to add to my tank.
30+lbs live rock -sounds good.. to give it that very full look I like to try to get as close to double the amount of gallons.. 30ish-40 lbs should fill it out very nicely
1.5 inch sand bed- that works
2 percula clownfish-sure
1yellow watchman goby-sure
1 mandarin dragonet-cannot be done please dont even attempt it.. this fish MUST be in a tank w/ AT LEAST 100 lbs of LR because all it eats are pods, and it will die in your tank. In your size tank I'd only go w/ 3 fish
1 cleaner shrimp-looks good
1-2 cleaner clams in refuge- dont know much about these
1 yellow cucumber. (tank or fuge)- dont know much about these
x number of snails- looks good but also add hermit crabs
a star fish- the only type of star that wlil survive long term is a serpent starfish. I have 3 in my 75 gallon tank, and they come in many many colors.. I have a bright orange one which is stunning. Do not however, get a "green serpent star" they can be terrors in your tank and eat your fish and or shrimp.
frogspawn- sure great coral, hopefully your clowns will choose either this or torch and host in it
torch coral-great coral great choice
zoos-always a good choice
shrooms- I love shrooms especially ricordia
leathers-not a huge fan of leathers myself but I do have a couple. They will work fine in your tank but I just feel like they are to large in my 75 gallon tank.. I cant imagine them in a 20 but if you wanna.. go for it!
star polyps- great coral.. spreads VERY quickly
brain coral- which type? I'd go for a open brain coral aka trach
hammer coral- also a great coral. It is just like frogspawn and torch.
Another great coral you dont have listed is candy cane coral.. its a beautiful LPS coral
4 inch sand bed in fuge
chaeto/or other plant
11 watt lighting in fuge. -this all sounds great
dont know what pump size-cant help you here
is that too much.
I'm not planning on adding all of these, these are just the things that I like. Or could I have all of these in my 20 gallon?
You may be able to manage but the stuff grows pretty fast so you'll have to frag stuff out.. I'd stay away from the leathers if I was you.. just because like I said before they are very large and tempermental.. not one of my fav types of coral.