If the parcel you sold was equal size and similar characteristics as the one with the residence, your land basis in both would be ~$35k each.

All things being equal (and they never really are) the price per sf is an indicator.

But putting less down increases your mortgage payment, and on top of that you have PMI.True, but triplexes pretty much always cash flow better than duplexes, all things being equal.

I usually put down 10% at 6% with a 20-25  yr am and the payment equalling about 6/9 of what they currently receive in rents. 

The 12.99% you are paying is about equal to what a hard money lender would charge around here.

In addition all lakefront isn't created equal there is town, type of water access, how popular the lake is, how well people know that lake.If you share more perhaps people can provide area specific advice too.

Condo's are equally ridiculously priced. 

I don't care how nice they refinished the basement, it is still underground with no view and not even equal to the above ground.

Total P/I payments would be $307,080 at the end, plus the $4,950 to close the first time around would equal a total of $312,030.Conclusion:From my math, even if I have to pay closing costs on the commercial loan every five years, I would still save around $100K going the commercial route.

You are first taking profit.So just figure that everything you take out will be taxable until you take out an amount equal to all your gain.