Many of the Agastaches reseed freely on their own and I found them pretty easy to collect seeds from- I usually got 3-4 seeds from each single bloom base. I just put the seeds on top of moist potting mix in small pots. Kept them moist and in sun part of day. So far have been able to keep them outside but in my zone, I am sure I will have to bring them inside when it freezes. I am really a beginner at this, but there is a lot of good information online, on this site and other places. This site has a "Propagation" forum where you might want to post a question. I decided to post in this forum since I am only doing Agastaches and Salvias. The way you are doing it sounds great, but as I said, I am very new to this aspect of gardening so my experience and knowledge is limited. Since they grew so easily for me, I would think you would have no problems since you have already done Salvias. Good luck.