Welcome to TFF Audicy, and especially to the Nano pages!
The thing about going marine, and or specifically nano's, is you do need to be more religous about maintenance, and to really know your stuff when it comes to livestock, and whats appropriate. You dont need to get it down to science level, so dont freak!
But just to a level where you know whats good form bad etc.
To start, id suggest you read the pinned topics at the top of this page and any in other marine related areas like Marine Reef and Chit Chat.
Here are some specific reads that could help get you off the ground!
-SH's (Stealhealr's) Nano Journal! A terrific base of knowledge and a step by step guide to starting.
24G Nano Cube DX Nano Reef Setup
To get you excited!
And this thread will probably answer ALOT of first timer and lerner questions you might have!
There are countless other journals to read like Sf05's, Matthew5664's, bunjiweb's and Skifletch's, not to mention im probably forgetting some more members!
As for the anemone, clowns dont need them. Besides that they arnt essential for the general well-being of clowns, they can host in a variety of different corals.
Anemones arnt safe in a nano. They require high lighting, ie MH's (metal halides) and these will cook anything in a nano, and you could fit one in the hood anyways!
In 12 gallons, a pair of clowns might be fine, until they grow hopefully into larger specimens. Then they might need re-homing, but for now, thats ok. Some smaller species of goby might be fine though, like the "Neon" gobies or Okinawan/Yellow Coral Goby, but only 1 or 2.
Hopefully ive helped you start out. Like many will tell you, yes, it is tougher, but the rewards are far greater!
I look forward to "trying" to answering anymore questions you might have!