ammonia should be 0
nitr*I*tes should be 0
Nitr*A*tes should be no more than 40ppm less than 20-30 is a good level
Pure is right, Under gravel filters arent a plus, all they really do is just pull debris deeper into the gravel bed. Most people who are new to aquaria get them, then once they get some experience they toss them.
Snails, will not be worth your time, the Clowns will love them and you for giving them a tasty treat. Btw hope you know clowns can grow to 12 + inches. (and they aren't as cute when there fully grown imho)
SHrinp, there are many kinds, i like GHOST SHRIMP, they are transparent so you can actually see the food they eat go thru thier bodies. they only grow about 1.5 inches i believe (someone correct me if im wrong)
Sand is awesome. I tried it once (usuing play sand from home depot) and hated it for the simple fact that it did show the debris and waste a lot. But after some time has passed i tried it again. This time i used TRUE AQUATIC SAND and i find that it doesnt compact like play sand does (which causes deadly gas pockets to build up) and i have cories in this tank now and they keep the tank soooooo clean that i havent had to do a vac since i set it up over 2 months ago. Your loaches will love sand. they have barbells that the sand will be nice and gentle for them to sift thru.
Gravel will definantly gather a lot of debris, however if you plant it suffiecently then you don't really need to worry about vacumming that much as the plants use it as a fertilizer.
Wish you lived in PA, i would love to take the gouramis off of you, they were my first fish, and have survived thru all the torment that i put them thru when i was new.
PH- UNless your trying to keep some fish that are PH dependant, most fish will adapt to your ph, its better to have a stable ph than to have it fluctuating. so i wouldnt worry to much about adjusting it.
Plants. Someones comment wasn't eactly correct. You CAN have plants in Sand, i do, you just need to be selective in your choice of plants and need to make up for what they are lacking, ie, sufficient lighting, ferts, c02, etc.