Where do you start as in what do you do technically or where do you start as in the process of doing it?
I would buy a select fire trigger control group, a full auto bolt and carrier. order up or build the jig for the drilling and drill up my lower, drop in the parts, test it for go no go and work on timing it.
As to What should you do business wise, maybe just send out letters introducing your company to the local departments.
Note, although it is done by many renting of post samples really isn't specifically allowed by law...not saying, I'm just saying - ya know.
If you need some sample letters, you can grab some off my website.
Feel free to use them and don't forget to change the name.