In my humble opinion (albeit I've only been at this for 1.5 years), 30% is probably good for vacancy/repairs/capex barring there is no major deferred maintenance.

In order to defer all tax you must purchase at least as much as your net sale. 

If this is the case I’m thinking that applying for the 5 year deferment sounds appealing so I can save up some cash.

Could be a simple as they've been deferring maintenance and you need to use a slightly higher number in your pro forma.I wouldn't do that deal, unless there's opportunity to raise rents and/or lower expenses.

The other part is the "reverse construction part where your QI takes title to the lot you want to build on and holds it until the value is high enough to absorb your 1031 amount.In order to defer all tax you must purchase at least as much as you sell and use all of the proceeds in the 1031. 

@Darsh Patel, If you want to defer all tax you need to do both. 

When it was rented at $700/month was that because of a negligent landlord and deferred maintenance?

So your two reinvestment targets to defer all tax in the 1031 will be to purchase at least as much as your net sale (contract price less closing costs and commissions) and use all of the net cash ( net sale minus the mortgage pay offs) in the next purchase. 

This means tax-deferred Section 1031 exchanges don’t count, except to the extent you recognize any taxable income.

@Scott Isbister The treatment of illegal suits defer on the city.