Welcome to the forum.
Firstly a 32 litre tank is really very small and not suited to a bristlenose, bristlenoses can get quite big I have had both males and females close to 20cm in length. Otocinclus might be ok (but in my opinion 32 L is too small for them), but they need to be in groups and can be tricky to get feeding on prepared foods, mixing otocinclus and cherry shrimp would be fine. However mixing cherry shrimp and or otocinclus with puffer fish is not going to work. The puffers are almost certain to see the shrimp as a tasty snack, and would more than likely bully and nip at any otocinclus.
For the tank, I would only get two or at absolute most a trio of pygmy puffers, assuming that you are getting them as juveniles and wont have reached sexual maturity. Try to replicate their natural habit as closely as possible with the limited tank size, so bog wood and leaf litter will be good as well as rocks to create caves for them to hide in. Plants could either be plants native to the same area as the puffers naturally occur making the tank a bio-type tank. Or you could just put in plants that are readily available to you. Plants like java fern, Anubis and maybe even a short growing val could all work. With the plants there is a good chance that snails may hitch hike in on them. This can be a good thing, since puffers like eating snails and actually need the hard shells to help wear down their teeth.
Other foods for dwarf puffers can include daphnia, earthworms, mosquito and midge larvae, and occasionally brine shrimp, they will also take bloodworms. Some people also occasionally feed them small amounts of squid and or mussels just for some variety and extra vitamins and minerals.
I know it can be very hard with a small tank to get stocking right as well as all the necessary water parameters like pH, gH and temperature, let alone filters that don't end up blasting fish all over the tank. But a small tank can also be very rewarding and the challenges being overcome give a great feeling of satisfaction. We are all here to help you in your fish keeping journey.
