Does anyone have experience with the recom rpx-1.0 or similar that could explain a few things to me?
PG is power good  - an output that tells you the regulator is happy.
AGND (analog gnd) and PGND(power gnd) follow the datasheet’s pcb layout suggestion. This dc:dc converter is not isolated, so the gnd is not broken between the input and output. You normally pay more for isolation.
Yes, select R4 for the required output voltage. You’ll need to ensure that the capacitors are suitably rated for your various voltages and heed the datasheet’s advice on layout