I find D3200 in Rodinal fairly horrid. Large crisp grain and little detail, but then again you are using a Holga!
Firstly I would figure out whether the exposure is likely to be over, under, or about 1000-1600, then decide on developer., If in teh region of about 800, Rodinal will be about right , but if above 1000, youd be better of with somehting generating more speed.
Last time I developed I used D3200 and rodinal 1+ 25 and will see if I can find the times. No point going more dilute IMO as the film is low contrast (so no worries with the rodinal straight line) and the grain wont get much finer than gravel!