another newbie tank

Without knowing too much about your proposed set-up, but assuming you end up with 8 - 9 gallons of water in the tank, this should be ok.
A VERY general rule to follow is 1" of fish per gallon of water, but again, a lot depends on what fish. Example: a 2" goldfish will probably produce a lot more waste than a 2" tetra.
Anyway, with faithful water changes and routine maintenance, it sounds like you will have a very nice setup! I look forward to seeing the replies of the true experts on this site.

-sj

Fiddler crabs might not work. They require access to the surface--and will climb up anything and everything to get it, and may escape. They really do better in a vivarium--a mix of land and water. Also, most need brackish conditions in the long run--and tetras and cories will not live in brackish water for long.

If I were setting up a system like this, I would likely go with a single, medium sized fish, and then 4-5 pygmy cories. The tetras and cories will be stressed in groups of less than 3, and more than that will overstock the tank.

ya I would say ditch the crabs for sure. They wont survive long and they are very good escape artists too. Your Setup might be able to work if tetras are smaller ones (neons, glo-lights), But If your tetras are bigger ones, OrionGirl's idea would definately be the best way to go. A small Gourami or Betta would do nicely in 10 gallon tank with Corys.

I would get rid of the crab also
The Gourami may get a little large for a 10 gallon ...mojo has some large ones in his pond....but this will not happen over night.

DON'T go by the 1"fish per 1gallon "rule" its not a rule its a mith

10"oscar in a 10 gallon?? You couldn't even have one tat large in a 55 for long.

but you can have very small fish that will follow the mith

more than one gold fish won't work in a 10 gallon but 10 neons will

There aren't many inverts that will work--the dwarf aquatic frogs are marginal, IMO, since they can be tough to keep well fed in a community setting. Others either require access to the surface, or will view tankmates as dinner, like crawdads. Crabs and other amphibians are not fully aquatic--they need access to the surface. Some newts can be easily accomodated--many are mostly aquatic, and will accept floating plants or wood for surface access--as long as these objects are far enough away from the lights that they don't bake.

There are shrimp that will work--cherry, amano, ghost, and if you are careful, bamboo or wood shrimp will all work with most fish. Tetras and cories, certainly. In a 10, you could do 5 smaller tetras, 4-5 cories, a couple snails, maybe one dwarf frog (be sure not to get the clawed variety, as they get much larger and will eat small fish), and 3-4 amano shrimp. Adding live plants would help out a great deal, as well. Simple, low light plants like anubias, java ferns, and many crypts would help deal with the bio-load, and make the fish more comfortable. Fake plants will help some, but won't help with the bio-load.