I heartedly recommend getting ALL of them. Partly in jest, partly serious.
One of the biggest problems with beginning bonsai is dealing with impatience while waiting for trees to grow. If you have a group of trees, you will have more frequent things to do. Otherwise you end up in a cycle of watering, then wait, water, then wait.
I recommend 60 or more, that way every week something will need something done.
You are in Brazil. The Serissa should be much easier for you to grow in your climate than us in the USA.
There are a couple members from Brazil, they might be able to give you help, I'll tag
@Clicio