You must have great taste because sparkling gouramis are so beautiful! That's a fish I've been wanting to keep for a while. I'm glad you're setting up a 10 gallon and moving on to more fish!
It is true that the bigger the tank the more stable the water parameters are, but it's also more of an investment and you need more space to devote to it. So you have to decide what will work for you.
In terms of which fish, I would start with the more common ones that you see in pet stores. Platies, danios, tetras and such might not be as exotic as others, but they are commercially bred and adaptable to a wide variety of water types.
Also you'll want to have a general idea of whether you have hard or soft water. The people at the fish store should be able to give you a general idea and that will orient you in the best direction. I happen to live where the water is very soft and the pH tends to the acidic side. I have lots of fish that like that kind of water. On the other hand, if I wanted to keep African cichlids, I would have to buffer the water because they need hard alkaline water. If your water is at one extreme or the other, stick with fish that will be happy in it.
Of the ones you are thinking about, well, you'll have to make a couple of decisions. The white clouds want cooler water and will not be happy at tropical temperatures. The sparkling gouramis need warmer water as do the otos. I don't know much about freshwater clams, but I don't think they are a good choice. Most are filter feeders and there won't be much for them to eat. If it dies it will pollute the tank pretty quickly.
A good gourami would be a honey or a dwarf I would think. Instead of white clouds maybe some neons or glowlight tetras? Otos can be tricky. They are wild caught and fussy about their water and they need algae to eat. No plecos either, they get big!
What kind of filtration and such are you planning, and have you researched the cycling process?
Enjoy your fish tank!