Arellano - Bond estimation: Selection between endogenous and predetermined variables

#1
Dear colleagues,
I hope everything is well.

I am running Arellano-Bond estimation (xtabond2) and I would like to ask about the selection of endogenous and predetermined variables.

1)There is any rule or test that I should follow to characterize an independent variable as endog. or predeterm.
2)How many endogenous (or predetermined I should put in the fields of the related window?
3) Is it wrong if I do not select any variable for endog. anf predeterm. fields?

Please find attached a photo of the related window.

Thanks in advance.
I look forward to receiving your responses
Take care,

Kostas