Defintely good idea, as matter of fact even adding it a week or two before would be wise.
I think 50 mg (oral) of both are ok to start with and then if needed increase pregnenolone, with transdermal I think around 15-20 mg is ok to start with.
Excessive DHEA converts to E2 a lot, so thats why I'm cautious with increasing DHEA more than 50 mg, pregnenolone also converts to DHEA as well, so increasing preg should cover it all- when progesterone reaches a top than you know thats enough. Only possible confusion can happen- when HCG dosage is to high it also raises progesterone a lot, which can make dosing of preg/hcg bit difficult.
For raising DHT there is DHT cream/gel.