(a) All the trials I've seen on continuous vs intermittent show that outcomes are the same for men without distant metastases. I guess your para-aortic LN puts you in the M1a category, but you mostly seem to be N1M0. For those with distant mets (M1), they couldn't prove that iADT was not inferior to cADT. So it's really a judgment call, but I think most MOs would go with iADT for you.
(c) There is no one best protocol for iADT. It's whatever you and your MO agree upon. Usually the "on cycle" period is 7 months - a year (Assuming your ADT gets your T down to castrate levels, and your PSA responds accordingly). The "off cycle" period can be a set time period, until your PSA reaches some benchmark (eg, 10), until your PSADT gets very fast (eg 3 months), or until your T level gets back to a normal level so you actually feel like you've had a vacation. Again, it is a judgment call.
(d) iADT is often begun as soon as it is decided to pursue salvage ADT. It begins with the "on cycle" of course.
(e) There is no standard nadir to prove adequate PSA response to ADT. In the Hussain study, anyone was allowed whose PSA dropped below 4 after 7 months on ADT. It can be kept going until castration resistance sets in.
You didn't ask, but a nice twist on iADT is bipolar androgen therapy (BAT) - cycling 3 months on ADT with 3 months on high-dose testosterone. It assures that the vacation is a good one, and may extend the time one can stick with iADT. It's only been used in a small clinical trial./pcnrv.blogspot.com/2016/09/testosterone-to-treat-prostate-cancer_5.html