For instance, if you are purchasing from a long-time colleague or friend vs. an unknown cold-call, could those scenarios require different services selected at closing?

Too cold, they can add their own rugs and take them away when they leave.You should consider bundling rent, all utilities and possibly internet/cable together at a flat rate.

The kid wants to move somewhere cold.

Then you can mail or cold call or both.Other cheap or free methods are driving for dollars, craigslist, Realtors, FSBO sites, expired listings, foreclosure sites and bandit signs if allowed.If you have the funds you can use billboards, newspaper ads, other offline publications., TV commercials, radio ads, motivated seller websites, SEO, pay per click/adwords, facebook, Linkedin, Youtube, and other forms of online advertising and boosted/promoted social media postings.Bottom line is integrity and consistency.

A lot of the research I’ve seen has been ambiguous about the requirements and it looks as if most investors simply cold call and hope for the best.

It's like investing in a Subway sandwich franchise- you can't be out scouting for new restaurant locations if you're behind the counter serving Cold Cut Combos.If you raise your vacancy budget from 5% to 10%, and you budget 10% for a property manager (which you should do anyway, even if you'll be self-managing), the monthly cash flow goes from $350 to $150. 

Additionally we don't have too much cold weather in Northern CA. 

They hate having to manage all the people they've delegated things to.With perhaps the exception of cold calling/ reaching out to property owners the other things you listed are generally high on the list of things that investors like to do, and where they can create the most value for themselves. 

I also do a lot of cold calling which gets me great deals.

For example, mailers, cold calling, etc.