Hi and welcome to the forum
Try to get the biggest tank you can afford and have space for. Generally the more water there is, the more stabile the water quality & chemistry will remain, and the better it is for the fish.
If money is an issue you can get large plastic storage containers and use them to rear up fish in. They are relatively cheap and come with a lid to stop the fish jumping out. You treat them like a normal aquarium except they are plastic and you can't see through the sides.
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If you have an established tank that has been running for more than 2 months, you can take half of the filter material from the filter and put it in the new tank. This will give you an instant cycled filter. Just make sure you replace the material you remove with some new material.
If you can't remove filter material from the established filter, use a rubber band or some string to hold some new filter material against the established filter material. Leave it here for a couple of weeks and the filter bacteria will start to grow on the new material. Then you can move this into the new tank and it will help to speed up the cycling process.
Liquid filter bacterial supplements can also help. I recommend double dosing them each day for the first week then that should be it. Try to add the bacterial supplements near the filter intake or filter sponges so they end up in the filter. Keep the bacterial supplements in the fridge.