One very important distinction about taking a loan from your 401k is the double taxation payback aspect.

There are about 20 CPAs and accountants on this site that specialize in real estate taxation. 

That includes knowing real estate taxation if you own rental properties.

When selling straight out seller pays--capital gain tax -depreciation recapture tax at max 25%-net investment income tax at 3.8 percent if his MAGI greater than 200k.

Would the next best solution be to pull data from my department of taxation and assesstment and study recent sales in various neighborhoods to get an idea?

No double taxation and your allowed vacations...

Will,In Maryland we have the State Dept. of Assessments and Taxation online.

side-bar to various sections of the existing getting started guide.I've started assembling some materials on what's different up North with respect to financing, taxation, etc. but have been too overcommitted to finish putting it together.

And the 401(k) is more favorable for investing using debt-financing such as mortgages due to exemption from UDFI taxation on real property.   

In all likelihood, flipping 1-2 homes per year with such a plan, considering that you are also personally flipping so many homes would expose the gains on those flips to UBIT taxation.