Offer for a pre-PhD visit, how to handle the situation with other PhD applications in the queue? I have received an offer to visit a lab for 4/5 months that could lead into a fully funded PhD. In the meantime I have other applications in the pipeline from which I will hear back in either a few weeks or a couple of months (just different educational systems).

I am excited about going to this lab but I want to wait to have all my offers on the table before commiting to a program. Also I am not sure yet if I will be able to develop in this lab the project I have in mind. However the PI of the lab is highly regarded in the field.

If I were to leave the lab I would want to leave in the best note possible not to burn my bridges with this person and institution.

I am sure the PI knows I might have applied elsewhere and also although it is likely that this visit will turn into a PhD there is also a small chance it will not.

What would be the best way to handle this situation in an ethical and correct way, and not disappointed anybody?

PS: I will get paid in this period but not as much as PhD student. Let me know if more information is needed.

EDIT: So apparently by the end of the visit I will present a PhD proposal, so I hope that at that point it will not be too late to answer other offers.
In general, I think so long as you and the PI in question are forthright about your mutual expectations, there should be very few problems.

If the PI who is offering you the position is planning on having you become a PhD student, then that should be made clear. Similarly, if you'd like to consider other options, then you should let your potential advisor know that a "competition" will be taking place.

However, since you said you'd be writing a PhD proposal, it's not clear that you'd automatically have a guaranteed offer for a position at the end of this position if successful. This should also be cleared up before you make a final decision.