Do you use the same percentage and set aside a chunk for each new property you buy, or do you maybe decrease the percentage as you get more properties and have a bigger chunk of money saved?

I purchased both as temporary residence hoping to rent them after I move out.

Leaving your job is likely to retard making money via rentals as the only way to do that successfully is via loans and your ability to get loans for rental properties will drastically decrease when you leave your job.Age is not required to retire, income is, so there is no set rule you need to wait 20 years to retire. 

In the mean time, you have missed out on many other excellent applicants.The 'rules' are a temporary substitute for judgement which develop over time.

It is also a big salary decrease!!

I think this is a very niche market and we are just trying to be creative in using part of our land in a temporary way, almost a sales lot in a sense.  

I don't want to speak to which strategy you should use for decreasing your costs, but I would recommend examining your tenant screening process if you are having to actually go through the whole eviction process that many times.  

Properties in good condition that are priced right are going to sell quicklyThe one caveat with a HUD home as there can be a small issue such as a faulty shut off valve that will prevent a buyer from activating the water and prevent an owner occupant from obtaining an FHA,VA,FNMA loan and thereby drastically decreasing the pool of buyers and thereby creating opportunities for investors. 

This is about right as there will be new meters installed, digging the meter pits, new supply lines etc.The question, do I spend the money on decreasing the expenses at the fourplex property or invest in another duplex for about $15k down which will provide about $3600/yr cash flow?

If you decide not to increase rents for several years, you will be losing value on your asset.Remember, if the market begins to decrease, tenants will expect you to lower rents.Gino