With my fresh build I'm going to use the hondata s300 v3... Trying to find the best route. I have my stock p72 ecu. Should I just buy the s300 module. Or the s300 ecu package.

 

Whatever is in your budget. If you want to utilize the crappy stock knock sensor circuit then send yours out to be socketed or do it yourself.

 

I'm not sure why this is a question. The P72 is a valuable ECU, and I assume you have one because you have an IAB manifold. Even if not, it's nice to have as an extra output.
Any local tuner should be able to install an S300 in your existing ECU for under $100. Purchase the unit and have it installed and tuned by the same person.