From my understanding, it might be more advantageous to refinance as a rental property at a lower LTV with income from two units, rather than as owner-occupied at a higher LTV with only one rental income considered.

I think you'll be hard pressed to get an ARV of $140k IMO...I'd expect something around $115k or lower.

Right now they are "high" (compared to 2020) and people "think" they are going lower. 

For investors, the current market presents a mixed bag: while short-term rental income may be lower, Miami remains a strong market for long-term growth as affordability attracts more tenants.What’s your take on Miami’s rental market?

Covering the mortgage isn’t an issue, but I’m considering factors like: Multi-Family: House hacking would help offset costs right away, but I’d likely need to put money into renovations upfront.Single-Family: Easier move-in with no immediate renovations needed, plus potentially lower tenant turnover once I rent it out For those who have been in a similar situation, what did you choose and why?

As you're just starting out in Austin, focus on learning the local market, particularly areas with good rental demand and lower entry prices.

Should I wait for Spring for greater inventory, or for lower rates to see if cashflow improves?

If you are borrowing $150k, rates will not likely drop enough for you to justify a refinance due to lower rates.

Most listings have 2.5-3% allocated to the buyers agent already written into the listing agreement but you could write into the offer something lower, adjust the offer price lower accordingly and then pay your agent directly instead. 

Alternatively, your in-laws could partially gift the property by using the annual gift tax exclusion ($34K per couple annually), lowering the sale price and their taxable gain.