The LOI is a great idea, I haven't been doing that but should incorporate that strategy for sure as well as providing more than 1 option in the LOI and stating the benefits of the seller with each option.  

I'm working in corporate America right now in the mortagge industry and am very well versed in mortages as a whole, but need assistance with entering investing in this area.

@Christopher Reynolds In general, there are many features that can be incorporated into a 401k plan, but are not offered by employers.

Has anyone used Guest Houses or incorporated them into their REI strategy?

While notes are different than buying the property, you do need to incorporate lessons from them in buying notes.

A close friend of mine that has been in real estate for decades took a look at my analysis in detail and after incorporating his suggestions (for example, he said the condo fee will include insurance for the common area and the building but the lender will require me to buy insurance for the rest...I hadn't factored this in) and your suggestions, my cash flow figure has swung from +200K to -227K.  

In your opinion what would be the most tax efficient way to start investing, for example would you recommend incorporating a ltd. company, if so under what jurisdiction?

I used to incorporate companies in all 50 States and DC.  

The solo 401k may be more advantageous if you plan to invest in real estate and incorporate debt financing (non-recourse loan).   

Would anyone consider a "cash for keys'' offer to the tenant, and if they agree, incorporate that into the estoppel letter?