So is data crunching - as an urban planner, I love using those skills in conjunction with Census data (and I'm oddly thrilled about the new Census this year) to track trends in demographics and real estate values over time to spot areas that are likely to see short and / or long term growth in both cash flow and equity. 

I use a spreadsheet to enter simple data in to use as a comparison and calculate the comps.  

I am wondering what are some resources, preferably free, to get market data for the area I work in?

As I start looking at new cities and regions, I am curious to know what resources, data points and indicators others are looking at to help inform their next investment area. 

What are some data points that can help build businesses credit, such as: having a Dunn & Bradstreet number, age of business, having a cashflow on the books, and having a physical phone line with a 411 listing.What ways can this help with flipping houses?

I know less then zero about real estate (and real estate investing) in London unfortunately, but I will say that your planned rent vs property price would fail a common test in the US called the 1% rule. 

Don't start moving the goalposts (i.e. by inflating the sell price or lowering the reno budget without data to support it; using 80% instead of 65-70% in the equation above to sacrifice your eventual return) in an effort to wedge a square peg through a round hole.Not every property you analyze works, and providing them with a "low" offer isn't taking advantage of them. 

@Anna Catron We are still 'testing' honestrenter; so far we've been very happy with tenant picks from that site.

@Steven N.hard question to provide insight on without additional data.  

Getting real data on lease rates and other market terms is extremely important with these properties, because you won't get real financials most of the time.