You can learn Reiki in one or more levels. You can choose how you want to do it, you either go all three levels in a row or you have a break in between these. It should feel right when it's time to take the course.
It is also important to understand that Reiki is not something you get through during a weekend course. Reiki is something you have to work with all the time. Therefore, you will get lots of cool knowledge and various tools that you can use to do the job. It is you who must do the job by practicing.
Many who go Reiki 1 do it for their own sake. They want access to positive and loving tools to be able to work with their personal development and have no intention of working with Reiki professionally. Therefore, there are no requirements to go to the next Reiki level.
Reiki is divided into three levels:
Reiki 3 - Shinpiden Master
Remember that you choose how many levels you want to go, but to advance to the next level you need to have passed the previous level. This means that in order to study for Reiki Master, you must have attended Reiki 1 and Reiki 2. However, it does not matter if you have read, for example, Reiki 1 elsewhere to attend Reiki 2 with me.