I would just take into account that a lower down payment will mean a higher monthly payment so be sure to run the numbers conservatively in order to ensure your STR revenue is able to carry your monthly payment with this higher mortgage cost. 

Some insurance companies offer policies specifically designed for owner-occupied multifamily properties, so it’s worth asking about that option.The key is ensuring both your personal residence and the rental unit are adequately covered.

But you want your policies to be fairly firm. 

They want to ensure against potentially lending on a property which may be destroyed/badly damaged.  

Otherwise, the deal (and all my earnest money/inspection costs) falls through.Money Spent So FarEarnest Money Deposit: $1,500Appraisal: $750Inspections: $1,050Survey: $580I’ve invested a fair amount already, and I really don’t want to lose this opportunity.Financial SnapshotMonthly Income: $4,500 (increasing to $6,000 by March).Monthly Expenses: About $2,000 total, including $1,000 rent (which I won’t have once I move in).Future Income: By June, I expect even more significant income from my business ventures.Debt-to-Income: Not too high right now, but my credit score is poor, so that limits quick loans or credit card solutions.Condition of the PropertyFull Rehab Needed: The house currently isn’t livable without major repairs.Seller Won’t Negotiate: I’ve already asked for an extension and concessions, but the seller is unwilling to help or budge on anything.Attempts So FarFriends & Family: No one can cover $25K.Down Payment Assistance Programs: I’ve tried multiple; none seem to fit.Co-Signer: Already have a co-signer on the mortgage.Personal Loans / Credit Cards: With my credit score, interest rates are brutal, and I’m worried about jeopardizing my FHA approval.Extensions: We’ve already pushed the closing date back by a month.What I’m Looking ForCreative Financing: Any reputable local lenders, credit unions, or community programs in Detroit that specialize in these types of last-minute shortfalls for buyers with less-than-ideal credit?

To ensure my replacement property value is at least $600k, I was considering putting the remaining $100k into a DST.

Each property is different, however an engineered cost segregation study typically takes about 4-6 weeks to complete in order to ensure a quality cost segregation study.HOW MUCH MONEY CAN A COST SEGREGATION STUDY SAVE ME?

It's lower than 1.5%, sometimes I price deals out conventional & DSCR, DSCR beats conventional pricing a fair amount of the time.The only catch is the prepayment penalty on a DSCR loan.

The 4-unit is 1/1s, fairly similar footprints. 

This ensures you lock in better terms based on the improved cash flow.