I intend to work hard on the SEO of the website while doing PPC, and just want to know how to build credibility so the site converts well. 

., TV commercials, radio ads, motivated seller website, SEO, pay per click/adwords, facebook, Linkedin, Youtube, and other forms of online advertising and boosted/promoted social media postings.Bottom line is consistency.

Now I have scaled to DM ,Door Hangers, SEO, and referrals from realtors.

I have seen a lot of pricing models for SEO for wholesale real estate sites and am curious what business owners/investors prefer. 

I see that cold calling, SEO marketing, text blasting and direct mail marketing is working with several of my investors.

Unless you have some serious skills with SEO and internet marketing, having a website is very unlikely to help you at the beginning of your investing career.  

The seo help is for the snowplowing business.

Have you tried generating a mailing list, SEO, or cold calling?

To answer your question about where to begin, if I was starting all over again I would first be setting up a strong SEO website and driving for dollars to find deals.

@Mary Seo  I haven't seen a recent list, but there's a link in the first post on this thread from a while back that has a pretty good list:https://www.biggerpockets.com/forums/79/topics/388292-list-of-all-books-mentioned-on-biggerpocketscom-podcast