Since lenders now ask for 2 years of prior tax returns, not filing could jeopardize your future real estate investment career, especially if your increase income this year.I also know that for the Schedule C the minimum to file is something like $400 net but I'm sorry that I can't find the answer for Schedule E.

I think the volume of folks getting into the business has increased which may be affecting your numbers. 

I have considered for several years the importance of general investing, but recently have become increasingly interested in real estate investing.

Say I'm able to complete the refinance, I would then like to immediately apply for a pre-approval with the intention of buying another property as an owner occupant via FHA financing as my family size will be increasing in 6 weeks and I will need more square footage in my living space.Is this something I could do? 

This book truly changed my life, so much so that I bought a copy just to give to my brother in the hopes that he at age 27 could take advantage of what I'd already passed at age 31 (he's single and doesn't own a house yet, whereas I'm married and have a home).I have to admit, when I started listening to and reading Bigger Pockets I was thinking all about increasing earnings and didn't understand why I would "rob" myself in the mean time and be "needlessly frugal."

For example, if we got a $100/mo raise (after tax), we might increase our monthly expenses by $50.   

Over time as my cash flow and income increase it’ll become easier and within 5 years of starting I should be buying 5-6 properties per year.

Especially with only 15% down.I've been seeing 10 year interest rates creeping higher and higher above 5% over the last few weeks.   10-year Treasury is at 2.77% today, so even 5.10% is only ~230bps.   30 year amort is also becoming increasingly scarce on smaller deals.  

Perhaps fix up a couple units, increase rents, live there for 1 year, then move on to the next multi family.

There is NO benefit for you to take that money up front, but they know that flashing a fat stack of cash will throw some people into excitement.