In the past 2 weeks, I have sent a little more than 150 yellow letters and have gone through 14 zip codes, starting with the most populated areas in San Diego closest to me.

It's based off of zip code so the prices are according to your area and are updated often.

I've bought more properties with code violations than without.

I'm buying REO's, so often they have the old combo lock boxes so they give me the codes and go look myself when I want there too.

I would check what the local zoning codes are first to be sure everything is in compliance.

Just throwing this out there as an owner of a 98-year old house, and with the admission that I am NOT a landlord or familiar with tenant laws there....Are the plumbing & electricity up to code?

What your local municipalities require for codes, rental registrations, whom to talk to.

They should be able to work out the couple of kinks Ive been having in automation as well as address the online application need.For every onewhile I've got a programmer doing some code work should I A: combine all of my steps into a single email that directs potential tenants to the pre screening page, they fill it out, if they answer correctly they are directed to the scheduler ORb: They get the first email that directs them to the pre screening page after they fill it out they get a second email directing them to my scheduler? 

Pulling permits means I would have to bring electrical up to code, possibly plumbing and who knows what else.  

Also, if your property is recent construction, code requirements will be much more stringent.