From my experience sorting out other peoples' composty bins I'd say -

Don't add:
Citrus peel ie grapefruit or orange skins - they take forever to rot and make the bin smell.
Egg shells. They just don't rot! Ever! (despite what the books say)
Potatoes (including peelings of indoor ones) due to risk of blight plus you get baby spuds everywhere that you use the compost.
Tomatoes due to risk of disease.
Any meat or fish scraps - you already know about that one, but I wouldn't put any sort of fish scraps in either, as it will attract cats. Is that a bad thing?
Plastic. Obvious, I know, but that includes the labels on fruit, plant labels, etc.
Big lumps of any one thing - mix and match is the way to do it, and just roughly chop up any large leftover vegetables etc that might be on their way to the heap.

So carry on soldiering!

The worms are an excellent sign (they should be skinny red ones, called Tiger Worms for some unknown reason), as is the fact that you can't fill it: if it sinks as fast as you add stuff, then you are definitely doing it right!

PS It really works best if you can arrange to have a second composty bin, so that when the one does eventually fill up, you can leave it to cook while you start filling the second one. Otherwise you find yourself having to sort through part-rotted stuff. My personal least favourite job in the garden.

Definition of when it's "done" : when you can't recognise any of the components.

Hope this helps! Oh, final tip (really) whether you have a black plastic one, a loose pile, or some sort of container, try to keep your layers level, ie don't make a pyramid in the middle, spread it out and use all the corners.