are you looking to add all of them eventually or just one group from the fish list?
I only have experience with two if the fish on your list -
Dwarf Corys (several kinds; pygmey and Hastsus) I love them and they are one of my favorite fish but they should be in a group of no less then 6. The more the merrier with these little ones. I have 12 in my 20g and 6 in a 7.5g tank; they are great fun to watch, on the move most of the time, bottom of tank to mid tank and the occasional dart to the surface. They school together some days and others they are off on their own. Very social and leave all my shrimp alone. The 12 group are much more active then the 6. It seems they are more comfortable in a larger group.
Oto's can be happy but they have to be in a very established tank from my experience. I tried them several years ago and only one ever survived more then 6 months and my tank had been running for 2 years before I tried adding them.
For cleaning I have a long finned albino bristlenose pleco - with the body at about 2 inches. small for a pleco and so very colorful (bright yellow). might not be what your looking for but I'd be careful with Oto's as they are tender fish to me.
Personally I love the look of the gertrudae and think they would be a winner for your tank and would be very happy with all the coverage the plants will provide when they grow in. I hear they are jumpers but with coverage and lower water level I suspect you will be fine.
on the others, Amano's are a great choice. But the assasin's (mine) are always buried under the substrate and I only see them once every few weeks to a month, just about the time I figure they are long dead one pops out. I have 3 in a 20g. I was over run with other pest snails and they have decimated the population in 4 months. It seems that i only have 4 nerites and 3 assassins now.
Good luck in your choice -it's always hard!