I'm having some coolant leakage but I think mine has to do with a couple newbies putting too much coolant in the system during a recent oil change.

other things:
1) I had a reman put in 6,000 miles ago. (included new h2o pump and thermostat)
2) The temp gauge never goes above half way.
3) The add coolant light has never come on.
4) car starts right up
5) never see the white smoke @ startup
6) took the filler cap off and started it up cold.... coolant quickly started to overflow but before I put the cap on (40 seconds after taking it off and starting it up) I didn't see any bubbles.
7) coolant is right to the top in the AST.
8) coolant is right to the top in the filler.

symptoms:
1) noticed leaking coming from in front of passenger wheel.
2) noticed a lil' coolant near front of car under fuses near the fans.

I've bought a 13 psi filler cap and a 13 psi AST cap and will be replacing them in a lil bit.

My questions are these:
1) should the coolant be to the top of both the AST 'AND' Filler necks?
2) if it's the thermostat, does anyone know a good site that describes replacing it?

 

The levels should be close to the top.

There are 3 bolts that hold the water neck to the water pump housing.
REmove those bolts, you might have to push the airpump belt out of the way.
REmove old t-stat and replace with new t-stat. I thinbk there is an o-ring you should replace too. Make sure you note which way the t-stat was pointed when you pull it out, place the new one in the same way. There is a "jiggle pin" on the factory t-stat, make sure the jiggle pin is placed at 12 o'clock. Refill coolant, this can be the tricky part, make sure that you run the car for a min or two and check it again.
The FD system can be a little difficult to burp, check several times
over next day or two AFTER the car has cooled down.

 

It might be too full as you suspected. When our cars are over filled coolant will overflow out of the overflow tank. Just keep an eye on it. If it doesn't go away then you have a problem.

The AST should be completely full or very close to it.

Also you should buy an aftermarket temp gauge because if you had noticed the stock gauge rising higher than half way it would have already been too late.