I'm going to elaborate again, sorry my posts are so long.
For starters, I agree with the loach choice, stick with the botia angelicus. They are not as aggressive as some of the others can be, and if planning to keep corys with the loach, you're going to need A LOT of territory down low in the tank, so everyone has plenty of territory.
For plecos, the only really "small" pleco for that size of a tank is the pit bull pleco, and again, I would only add 1 pleco. If you want multiple algae eaters then stick to the otos. The otos are much slower growing, and they do eat a lot without bothering the plants. Otos are known to eat some of the hair types of algaes that other "algae eaters" won't touch. Their more varied diet accomplishes two things: healthier fish and a much cleaner tank.
The last tank I kept otos in was a 30 gallon. I had 3 of them in there for many yrs (at least 6), and I never had to scrape the glass. That was my 30 gallon show tank, and they shared it with algae eating shrimp, 1 clown loach, a few mollies and white clouds, a single diamond tetra, and 2 black tetras (all the fish were orphans). The tank was fully planted, and I had to pull/trim java moss every two weeks to keep it from taking over the entire tank. I had rock structures along the entire tank, built quite high in places, and everything thrived. My maintenance level was nil... I did a water change about once/month and my nitrates were always below 20. The fish ate every other day. It was my easiest and best tank until I found homes for all of the fish, eventually.
Anyways, the point is, I never had to scrape glass with those guys, they did all the work for me. I have only had 2 types of pleco that did such a thorough job, and only one of those was somewhat plant safe, and neither small enough to keep in your tank.
As for your current list:
3 cory cats
a couple dwarf chain loaches OR 1 botia angelicus
otocinclus (amount?)
1 blue coral platy
1 gold twinbar platy
cardinal tetras
If only going with 1 of each of the platys, go with both males. Then you will avoid breeding issues (unless you intend to set up another tank for fry and have an outlet for them within a few - 6 months) this would be the best choice. If you intend to breed, please do this much research about the breeding habits, too. They breed ALOT!!! Thus, with habits as they have, 2 females for each male is the ratio to keep. There is a thread here somewhere that I posted a picture into to help identify male from female. Maybe Blue can help to find it for us?
Watch the cardinals with the platys, and with the water params. With cardinals you'll need softer water, (the otos and pit bull pleco will also thrive in softer water... pH about 6.5 is good) but you may need to acclimate them a bit longer, depending on what conditions they are coming from. Many LFS's don't provide softer water for them, and the survival rate is low. For the fish that do go home, the change from low pH to high pH and back to low is usually too much for them, and they die within a few days. If its the color you're after, the neons would be your better choice, and the neons should be fine with the platys and softer water, too.
3 cory cats is a good number, it sounds as if you're narrowing things down. Keep in mind that with corys and loach in the same tank, they will compete for food, you'll need to make sure everyone gets enough without making a mess of your tank.
