Umm I'll go for the easier one first, Ethos - chocolates get to about 3", three-spots up to 6". I'm not sure which of the two exactly you were reffering to.
Now DMan99:
The single fin below the body, just before the tail and behind the long ventral 'feelers' is called the anal fin - basically because it is positioned beside the anus where all the poo comes out (now that's memorable right?
). However, it is actualy the dorsal fin (the fin at the top) that is more reliably used to sex three-spot gouramies. Males have a longer, more pointed dorsal while that of the female is rounded and shorter. You can also see (if you have both sexes) that females are deeper-bodied and wider when viewed from above when compared to the more 'stream-lined' looking males.
How many gallons is a 30"X12"X15" tank? Or litres... I'm terrible with dimensions.
It sounds like a 20 gallon?
I'm not clear as to whether this tank you have set up is a seperate tank to the main tank or not. You see you need 2 tanks to breed three-spots - one to spawn and raise fry, and one to permanently house the adults.
I'm just going to say that the tank you have set up at the moment will not work to breed them in. A selection of reasons why?: too strong a current, filter will suck up the fry, should be bare-bottomed to make picking up eggs and finding food easier for the male/fry respectively and so on. You also need to be prepaired to feed the very, very tiny fry when they first hatch out - infusoria may be needed at first (or try commercial liquid foods), then prefferably microworms (but you can try newly-hatched baby brine shrimp though I personaly don't like to rely on those as they can cause health problems if the fry manage to swallow one of the egg shells).
What I can say is that your feeding of the adults sounds good. I would also raise the temp. to about 80 deg F gradualy though 78 is usualy fine for three-spots. This should realy be fine for conditioning them. Feeding them the occasional veggie is good too - peas, zuchinni, courgette, cucumber and even lettuce - blanched or shelled accordingly - are often appreciated.
Now, as I don't, to be honest, realy want to type this out again, (ask if you have any questions though by all means), here are links to a few threads in which I posted about breeding gouramies in some detail. There are still things missing though so do ask if you aren't clear on something.
Here:
http/www.fishforums.net/index.php?showtopic=93178 (about pearls but three-spots are pretty much the same except they tend towards being more violent during spawning).
and:
http/www.fishforums.net/index.php?showtopic=91562 (about dwarfs, but, again, very similar process)
Those are the ones I can find at the moment.
I'm sure there are many more threads about breeding gouramies. Those in the trichogaster and colisa genus are all very similar as far as breeding behaviour goes so maybe do a search on them (three-spots and all their color morphs, pearls, moonlights, snakeskins, dwarfs, honeys, banded and thick-lipped...)
There's also a pinned topic (I think) on breeding dwarf gouramies. The process is similar though the person who posted may not necessarily have the same viewpoint as I do on how to breed them so do keep that in mind and do some more research to see what other people think as well.
BTW, info on breeding gouramies is generaly limmited but there's an amazing number of betta-related articles on the net. These can be used as refference as well as they are both bred in a very similar way - the only main difference being that bettas will kill each other more readily.
Good luck!