You already have experience in publishing. Could you please describe in more detail what your question or problem is in this case?

Can I use the same data twice? I don't know if I can use what I've gathered now with the new data that I'll add later to them.

I think this should be possible if more data will be added later and more results will be gained. In your later paper, you may refer to the first one saying that "prelimary results were presented in ...".

Many thanks for your answer Wolfgang.