Im not 100% sure about the heater...

but i can suggest fish for small tanks... well nothing for 1gal.. why not get some small shrimp for the 1gal... cherry shrimp maybe.

In a 5gal you could keep a betta or a shoal of mircorasbora.

10gal- endlers, guppies, neons, kuhli loaches, dwarf puffers(species tank), African dwarf frogs, otto's Well there lots of small tetras to choose from...
Usually id only have 1 shoal of 6-8 small schooling fish in a 10gal then add a few botom dwellers.. some people add cory's but i think there better off in 15-20gal tanks. African dwarf frogs are great additions to small tanks.

As far as i know 5-10gals are pretty cheap... I think a 5gal with a betta would be a good option till you can afford a bigger tank...

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211gal- 4 Clown loaches, 1 African butterfly fish,4 Dension barbs,2 Jewel cichlids,2 Firemouth's, Green Terror, sailfin pleco, L142, 2 cory's Candy striped pleco,4 Siamese algae eaters, 14 Black widow tetra's, Striped Anostomus, 3 Hoplosternum thoracatum, Fire Eel