the inch per gallon rule is just a simple thing to tell people who don't want to think about it and won't wait for an explanation of what goes into properly choosing tank,filter, fish, feeding, maintenance cycle.
Overstocking is ok as long as the maintenance is proper, the filtration is adequate, and you don't have fish that are aggressive. Understocking will lead to healthier fish, easier maintenance and more likelihood of breeding (if that's what someone is trying to do)
As far as your list it's fine, I'm not sure if you meant 2-3 inch per gallon or 2-3 gallons per inch.
that should be fine providing that you keep a clean, tidy tank
That'll be fine, the tiger barbs could get nippy, but for sizes and everything that tank works fine!
It's AMAZING Good luck to you. http://inhut.info/357123/with-plant
tiger barbs need schools of 8 or more
rasboras, tetas and glofish/danios need schools of 6 or more
yoyo loaches need shoals of 4 or more and get to at least 5 inches.
That would over stock your tank.
Their is no rule 1 fish 2 inch red fish blue fish.
You keep fish that are good campanians and do not show signs of stress form overstocking and the levals of nitrate, ammoni, and nitrie are safe with normal filtering an cleaning.