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

I'm not sure which one I have to replace, if any. 

Here are a couple of ways you could structure the deal:Lease Option with Seller Financing: You could lease the property with an option to buy later, allowing you to rehab it while giving the sellers time to find a 1031 replacement property.Seller Financing with Deferred Payment: Structure the seller financing with no immediate payments, allowing you to refinance once the property is appraised, and the sellers can complete the 1031 exchange when ready.Escrow Holdback: Transfer the deed into an escrow account, giving you control without immediate transfer, so the sellers can take their time with the 1031.Third-Party Facilitation: Use a qualified intermediary to hold funds and facilitate the 1031 exchange while you refinance.These options allow flexibility for both you and the sellers.

Based on rough assessment, the following is needed just to get it listed:NeedsLowMidHighRoof$7,747.00$12,580.00$26,037.00Siding$20,000.00$25,000.00$30,000.00Windows$9,000.00$12,000.00$18,000.00New Deck$8,000.00$10,000.00$12,000.00Roof Leak Repair$2,000.00$3,500.00$5,000.00Mold Mitigation$1,000.00$2,500.00$3,500.00AC Units$13,000.00$15,000.00$18,000.00Carpet Replacement$2,500.00$3,500.00$5,000.00Kitchen Remodel$5,000.00$10,000.00$20,000.00Total$68,247.00$94,080.00$137,537.00Due to lack of capital to fund these repairs, I believe the best option is to find an investor looking to flip. 

Unless new companies create replacement jobs in the city requiring similar skills and pay comparable wages, your tenants may be forced to take lower-paying service sector jobs.

February may not be the best time to find a replacement tenant, so you may want to go Month-to-Month (MTM) until April or so.

Do you save three months of vacancy for each unit and $50,000 for the roof replacement?

If I can replace the bathtub with a shower, I'd be able to make the bathroom feel larger.  

We have seen maintenance costs skyrocket over the past 2-3 years and every case is different but here are some general guidelines for reputable (non-crackhead) investor level pricing in our area of operations:Furnace and A/C replacement with lineset for standard 3 bed 1 bath bungalow.

@Jack Cottrell You Vacancy & Maintenance percentage are aggressive and may only work for a Class A rental/tenant.If the is a Class B or C rental that will attract Class B or C tenants, you should strongly consider increasing those percentages.NOTE: we deal with a LOT of Class B & C rentals, so we replace "Vacancy" with "Vacancy/Tenant Nonperformance".