Right now with the one property your gross rents are $1000 maybe $1200 if you raise them.So that can you buy with your 1031 that will provide better gross rents and then back out any additional financing costs.  3 50K down payments on three new 200K houses might provide better cash flow over all considering that borrowing is so cheap these days.   

your running costs will be 50% maybe 55% or maybe 45% of gross income.. then pay your mortgage.. 

Remember, if you have not yet claimed the investment property income on your taxes, lenders will typically use 75% of the gross rental income from the lease to qualify you. 

STR gross income should be FOUR TIMES or higher than the LTR rent?

I don't have any experience with self-management personally as even when we only had the one unit I used a PM for 10% of the gross rent per month (well worth it in my opinion if financially it makes sense). 

MONTHLY                                           YEAR 1 Rental Income:            $5,083.50                                            $61,002Vacancy Rate:             ($1,700) if we live in this unit              ($20,400)GROSS INCOME:           $3,383.50                                            $40,602ASSESSING YEARLY EXPENSESProperty taxes: $1,055 x 12 = $12,660Insurance: $166 x 12 = $1,992Maintenance & CapEx: $338.35 (at 10%) from occupied units?

My utilities are generally 30% of gross rent. 

I put this breakdown in my archives to keep track of what actually occurs as time goes on.Rental Income $125,400.Property Taxes $21,875Gas $1300Trash $1,400Water $3,000Insurance $3,600Net Annual Income $940,000X 10 Years = $140,000Now, I look at profit with annual rent increases plus increased property value that results from rent increase multiplied times the Gross Multiplier over a 10-year period.

A 100% tenancy rate does not mean your too cheap, not at all, that's a gross over-simplification of data.

They offer great multiple buying the business but pound them on lease terms.Hopefully roof and structure is newer or you could have hug expense in the future.You do not have a NNN lease you have at best a NN lease or modified gross lease which is not as desirable because you can have UNKNOWN current and future obligations for expenses that are hard to quantify but usually a fixed lease rental schedule.Insurance might be high because building is older or it's a single policy versus a larger property owner that gets bulk discount pricing for adding another property to insure once a certain threshold is met.