Corys really like company, and prefer company of their own species if possible. If it were my tank, I would add at least 3 more Swartz's corys. They are schooling fish, and are only at their best in a group of 5-6 of the same species. Of course, with all those loaches and corys you have an aweful lot of bottom dwellers. The 1" of fish per gallon rule (guideline, I should say) does assume you are distributing fish throughout the tank. Right now you seem very "bottom heavy."
I think gouramis are a good choice, but I would be nervous about 3 pairs in a 29
gal. Unless I am mistaken, all of the dwarf gouramis are the same species, they have just been bred to have different color patterns. What I fear is that you are going to see a lot of aggression among your males. If your tank is really, really heavily planted (including some floating plants) you might be able to get away with it (so they can each establish their own territory), but I am not terribly optimistic. Furthermore, if you are thinking m/f pair for each of those gouramis, then if any of those pairs actually do spawn, that might have the net result of even more aggression as the fish defend the eggs. I have even read reports (can't confirm this myself, just passing along what I have read) of a male gourami killing the female after spawning because the tank was too small for the female to get away and the male perceived her to be a threat to the eggs. Not sure if that was with dwarf gouramis or another gourami species. Perhaps someone who has kept multiple pairs of gouramis in the same tank could offer some insight here.
Perhaps another option would be to add one pair of gouramis and then consider something that would be a "mid-water" dweller. Something like cherry barbs might be nice--they are on the timid, peaceful side, they are low-activity fish, and the coloring on the males when there are females around is truly stunning.
When the day comes for the loaches to move on to another tank, you would have room to add a school of 6 of so mid-dwellers...most tetras, barbs, etc. would fall in that category. But with the fish you have now, adding yet another school of fish would probably be overkill. That is one reason I suggested the cherry barbs--they don't need to be in schools, in fact, many say they do best as a male/female pair or 1 male with several females.