What can I expect? Will progress continue or accelerate? Can I maintain a partial herbal regimen while taking hrt? Should I just stay on my herbals since I’ve I had nice results?

HRT is more effective than herbals. When taking HRT, avoid herbals because the herbs will blocks your receptors and nullify the HRT.

I'm just a beginner here but it seems to me you might be at a mature state of growth. If your growth is stalling out, HRT might not help that much. However, you won't know until you try. 

After 5 months of herbals, including PM, I've come to believe that HRT is a cleaner, less risky approach because HRT prescriptions are manufactured at a higher standard and presumably are purer than the unregulated stuff we take.