I own a home and built an ADU in the back yard 2 years ago and net $1000 per month positive cash flow.  

Well technically, I guess you could, but you would need to disclose and it is unlikely any LPs would be okay with that, let alone your lender willing to take a second position on a deal. 

We thought keeping the old townhouse because it can generate positive cashflow or maybe a little negative cashflow if something needs to be fixed.

I can definitely tell you there's still a lot of positive cash flowing and 1% rule deals and you get amazing appreciation.

I would sell the properties.4 rental properties over 3 years won't make you much money.Maybe 100 per door per month in cash flow and a matching amount in appreciation.That is $9,600 over a 3 year period assuming you have SFH's.You are improving your ability to make more money in a better position hopefully when you complete your master's degree.You will make that $9,600 working 2 weeks.The sale of the home will hopefully allow you and your wife be stress free for those 3 years helping you make a higher hourly rate.

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I’d also analyze the deal based on if the numbers will return to the positive side once you move out.

:Class A Properties:Cashflow vs Appreciation: Typically, 3-5 years for positive cashflow, but you get highest relative rent & value appreciation.Vacancy Est: Historically 10%, 5% the more recent norm.Tenant Pool: Majority will have FICO scores of 680+ (roughly 5% probability of default), zero evictions in last 7 years.Class B Properties:Cashflow vs Appreciation: Typically, decent amount of relative rent & value appreciation.Vacancy Est: Historically 10%, 5% should be applied only if proper research done to support.Tenant Pool: Majority will have FICO scores of 620-680 (around 10% probability of default), some blemishes, but should have no evictions in last 5 yearsClass C Properties:Cashflow vs Appreciation: Typically, high cashflow and at the lower end of relative rent & value appreciation.

I agree with @Nathan Gesner & @Caleb Brown, let your job help fund your first deal while perhaps searching for a more fulfilling position elsewhere.1.

Then I moved on to purchasing my own rentals which are all clean BRRRRs since there are still deals here that hit the 1% rule, positive cash flowing, with lots of appreciation.