@David Edwards, You already have a mortgage and insurance I assume.Those give you 2 layers of protection already.

(It has a layer of lead paint underneath that but the latex paint is generally in good condition, so only a tiny fraction of the lead on the exterior is exposed.)

All the profits pass through up to my holding LLC and profits expenses as much as possible in each layer to limit taxes.

The information they give you is freely available and I got more out of reading BP than their sales pitch masked as a ‘workshop’.

According to the inspection report, there are 3-4 layers of existing shingles under the newly installed roof.

Usually the next hurdle is off street parking, around here 2 off street parking per unit is common though some places are requiring 2.5 or 3 per unit.Next is code issues including fire separation;  the 2 units need to be separated with a fire barrier, usually they will accept 5/8 or 3/4 inch drywall; or double layer of 1/2 drywall. 

My only fear is the new paint smell is masking the nicotine smell.

I know there is two types of oxygen barrier from pex, one has the aluminum barrier infused in an inner black layer and grey outer layer, the other does not, and has a different type of barrier but it is 2 separate walls.

We are considering doing insulation on the ceiling with two layers of 5/8 drywall with green glue in between.

If your roof is on plank here your best choice would be to replace it not repair or do another layer.