bettyboop: the timing of when you start long down reg is to get best value from the drug. if you start on day 21 you can be pretty sure you'll get a month's worth of DR from it. if you start a long down reg at a different time of the month, it can take longer for your body to finish the cycle it is already doing so you might not get down regged until the end of the cycle. starting on day 21 means that you should normally be down regged within about 2 weeks.
the longer you down reg for, the more likely it is that your ovaries will be very shut down when you start up again. So after a couple of weeks, the down reg probably wouldn't be terrible but asking your ovaries to wake up quickly after 3-6 months might be asking a lot?
I did take cordyceps on long down reg and it was ok. if your ovaries aren't going to making estrogen/testosterone on long D/R, I can't see how cordyceps would change that?
whether you need to use buserelin or antagonist during your Tx will depend on whether your LH is still shut off (how long ago you had your last prostap when you start). I would GUESS that penny wouldn't put you on anything when you start your stimms, but might add antagonist after a few days?