Not an economist who has studied these issues, just and armchair intellectual here.I bought a house in my neighborhood and my realtor thought I should airbnb it. 

Scenario 1:Rate: 9.375%Monthly Payment: $1,185.31Closing Cost: $12,768.53Broker Fees: $2,417Lender Fees: $2,170Cost to Buy Rate Down: $0Escrow Fees: $2,797.501 Year Hazard Insurance: $1,044Impound Account: $1,598.04Appraisal Fee: $500Down Payment: $48,000 + $10,526.54 (30% down + closing costs)Total Cash to Close: $58,526.54Scenario 2:Rate: 8.875%Monthly Payment: $1,144.87Closing Cost: $12,768.53Broker Fees: $2,417Lender Fees: $2,170Cost to Buy Rate Down (1%): $1,120Escrow Fees: $2,797.501 Year Hazard Insurance: $1,044Impound Account: $1,598.04Appraisal Fee: $500Down Payment: $48,000 + $11,646.54 (30% down + closing costs)Total Cash to Close: $59,646.54Scenario 3:Rate: 8.625%Monthly Payment: $1,124.87Closing Cost: $12,206.54Broker Fees: $2,417Lender Fees: $2,170Cost to Buy Rate Down (1.5%): $1,680Escrow Fees: $2,797.501 Year Hazard Insurance: $1,044Impound Account: $1,598.04Appraisal Fee: $500Down Payment: $48,000 + $12,206.54 (30% down + closing costs)Total Cash to Close: $60,206.54Scenario 4:Rate: 8.375%Monthly Payment: $1,105.03Closing Cost: $12,768.53Broker Fees: $2,417Lender Fees: $2,170Cost to Buy Rate Down (2%): $2,240Escrow Fees: $2,797.501 Year Hazard Insurance: $1,044Impound Account: $1,598.04Appraisal Fee: $500Down Payment: $48,000 + $12,768.53 (30% down + closing costs)Total Cash to Close: $60,768.53Which of these options do you think is most suitable, given that I plan to pay off the loan sooner rather than later?

My advice, don't go for a homerun, a base hit is just fine.. buy something solid and get educated about your market.Its sounds like you are spreading yourself a little thin with all those markets to study. 

Does anyone know if you can use a cost segregation studies for STR properties that you may have outside the US (and use it against your US W2 income)?

How much time is needed to process the accounting on this? 

So that will be $35/month in costs + that you will need to account for who paysJust my 2 cents

You need to know buyer has their own money they just want to use someone else's money to buy.Big difference between someone with 500k in their bank account wanting to use an HML and a buyer with 5k to their name and putting up 1k non-refundable on a wing and a prayer.If you had multiple investors you likely should have screened your investors much harder to see who looked the strongest and could perform.

There are specific rules for 1031 exchanges including:The replacement property must be identified within 45 days of transferring the relinquished property.The replacement property must be received within 180 days after the transfer of the relinquished property or the due date of the taxpayer's tax return, whichever is earlier.Special rules apply for exchanges between related parties (defined in § 267(b) or 707(b)(1)).Real property located in the United States and real property located outside the United States are not considered property of like kind.Cost Segregation StudiesA Cost Segregation study is an IRS approved federal income tax tool that increases near term cash flow by utilizing shorter recovery periods for depreciation to accelerate return on investment.

Any bank in MA should be able to start an escrow security deposit account for a tenant.

On another note your “numbers analysis” may not pan out when you take into account repairs needed as revealed by inspection reports; and this may be the reason you don’t move forward without further seller concessions.