I did my first 70.3 this year in July after starting with TR in Nov 17’. I did low volume SSB I & II, Half Distance Tri Base, Build, and Specialty.
Hindsight being 20/20, I would not follow that progression again. The SSB I & II was great but following it with Tri Base felt to easy and I felt like I wasted 8 weeks of different training stimulus that could have grown my FTP further. I did enjoy the HIM Build and Specialty though.
If I had to do it over again with the same amount of time, I would do Century Specialty (currently on this plan and it alot of sweet spot and tempo & great for training to push the pedals hard for a good amount of time), SSB I & II, HIM Build and Specialty. Just my 2 cents.
Good luck in your training!