This vary heavily town to town. 20% down is great if buying strictly as investment but if you have a way of owner occupying I would explore that route and apply the 20% down to increasing value of property and instead using low money down loan. 

Mgt, Landscape/Snow, tax, insurance, utility then debt service. 

From a tax implication standpoint, it can be tricky but if done correctly, not a problem.

Agreed that leaving money in the deal is ok.

Some buy to park money, others do 1031 exchanges or they simply buy them for a tax write-off. 

At the end of the day; you need more money to do something like this.MAX LTV on new builds is 80% LTC, Meaning if the build is $550,000 and Land is XAdd ($550,000 + x ) * .8 = LOAN AMOUNTYou would need to come in with MINIMUM 20% of the cost in addition to closing costs and reserves, $80,000 is not going to cut it for this project.

There are also some benefits to leverage such as tax breaks that lowers the effective cost of borrowing the money.

The sellers you are dealing with in these situations don't deal with prorating Taxes, or any other kind of prorations, that is what an escrow agent does. 

Zero capital gain tax, next to zero income tax, property Tax is super small.  

There are also additional costs of operating and maintaining an LLC, like separate bank accounts, annual report filings, tax filings, etc.2.