Serissas can be very difficult, depending upon your climate, but they may work for you. Also look into potentilla, they are impressive bonsai and I think that they work in your climate? Whatever you try, buy it cheaply, and make sure that it is healthy to start with. Bonsai is about patience, it works best if you learn to curb your impulses.
Look at what is available easily in nurseries, and in peoples yards to see what grows well. If you choose something that is hard to keep alive, and it dies, you will be discouraged... but if you choose something that lives and grows well, you will be more likely to move into difficult trees.
I keep my minis in a sand tray in dappled shade, they can do pretty well that way. If you really, really want minis then you can try this. But you have to get trees that are pretty small with big trunks, and then slowly work them down into the small pot. It may take three growing seasons to do this, depending upon the tree. Or, you can take cuttings and them pot them into small pots fairly quickly. Minis need to be checked every day, sometimes twice a day in the summer, and extra care needs to be taken to make sure that they are in the best possible conditions. Just a few scale bugs or aphids can do a LOT of damage to a mini.
Starting so young, if you can keep with it you will have tremendous trees when you are older. And a lot of experience. Bravo to you!
Joanie