For example, if the main drain has a blockage and filled with water, and someone unknowingly flushes the toilet, the positive pressure created by the flushing action had no where to go due to the blockage, in a conventional atmospheric vent the positive pressure can just be relieved, but not with an AAV.In some jurisdictions, they allow you to upsize the drain line in order to allow part of the drain to serve as a vent.Also, try to explore an option where a conventional vent can be implemented in the island, but creatively disguised as a support beam, a decorative pole or something.

I have been in business for about 2 years doing residential remodeling and some commercial finish out work.

Here is what I mean.We can get good rehab-prices on the plumbing and electrical work, but often these contractors are not able or willing to do the drawings needed for the permit.We have found contractors who will do the drawings, but they are also busy with new construction and retail remodeling.

I am planning on putting in duct work for a natural gas unit to heat the main floor and the new basement remodel (which will all be one apartment).My question is what should I do with the upstairs apartment?

Do a couple like that first, then advance to more involved rehab (paint, flooring, kitchen and bath remodel).

Trying to put my remodel budget $$$ where it counts the most and this seems like an area I can save a little money in.

With 20% down its only a difference of $100 on the down payment, but that $100 could have bought the toilet that needed to be replaced. 

The house was totally remodeled in 2010 from the ground up.

There's also the method of living in a house you're remodeling as a flip every other year.

Do you have a spouse or kids that will have to live in the place while it is remodeled?