imagePROGRAF 1000 and PPI in Lightroom

[rjsphd]

I use Lightroom Classic and an iMac to print with my Pro-1000.  The PRINT module of Lr  has a "Print Resolution" checkbox.  When checked, you can chose the number of PPI.  

For optimal output on a variety of photo papers:

1. Should the box be checked?

2. If so, what number of PPI should be used?

3. Does it change with the size of the print?

Many thanks in advance,

R