Hmm. What are your water PH and hardness readings. None of us can go about recommending fish for you as we don't yet know the specifics, some fish such as boraras brigittae, and boraras merah, thrive in soft water, while others such as mollies don't handle soft water very well
They do need sand or very fine gravel depending in the type. Typically larger types such as bronze, albino, peppered, or Julii need sand or fine pebbles but the dwarf species such as Habrosus, pygmaeus, and Hastatus only do well in sand. For the larger species you would need a minimum of 4-5 but for the smaller species you would need a minimum or around 6-8. Please post a specific species so we can narrow down requirements for it.
Ottos are very, highly sensitive fish with many needs and have to have a high amount of algae to graze on in order to thrive. I would not recommend these species unless you have the commitment. They also thrive in planted tanks. 2 isn't enough either. For best behaviour and happiness along with minimal stress, the required number is 3-5
Depending on the Corydoras species and Plecos. Yes, the shrimp would be fine, but with 4 large cories or 6 small cories and a Bristlenose I honestly would think you are over stocking. I would recommend either taking the Corydoras or the Pleco out of the list. Preferably Plecos as Corydoras are much more rewarding fish IMO/E
A dwarf Bristlenose should be okay depending in what else you have in the tank, if you already have the cories. I woudlnt recommend bristlenoses. They have an extremely large bio load for there size and eat a lot. With sand the amount of poop can also be very unsightly, since debris settles on top of the sand instead of falling through as it does with a gravel substrate