Do I need to pay the artists?You need to pay the artist if they charge a commission fee. Art shops on CS are required to have a CS payment option available so if you can not pay in real-life currency there should be a CS payment option as well. You can also look for free art
here.
How do I know if my species is too close to someone's closed species?If you came up with an original idea you should be fine. It is alright to take inspiration from another artist's ideas as long as you are not copying traits that are exclusive to their characters.
I can't draw good so do I also need to draw?You can draw the character yourself or you can commission someone to do it for you as long as you credit the artist.
How do I do traits and rarities?That is your choice because these are your characters and your rules. Your species can be as common or as rare as you want them to be. Some artists make their species inherit certain genetics and rarities based on breeding percentages so you could use that as an idea.
Does the story need to be super long?It can be as short or as long as you want it to be. I recommend keeping the story brief while covering all the important information.
How do I make currency for the species?This is also your choice because these are your characters and your rules. One idea is to have a currency that is exclusive to adopt your species and it can be obtained in exchange for stuff you want (e.g. the adoption fee is five tokens, one wish list pet equals one token, for every five wish list pets they give you they can adopt one character - this is just an example so feel free to come up with your own ideas).