Compounding on one another sure that will have a big impact on the market but there are a lot of factors at play.

While less than 10% of the mortgage industry offers 40-year mortgages, here's something to factor in: they often come in with a rate increase of 20-35 bps.Assume 35 bps.$300k mortgage at 7.25% (30-year): $2,046$300k mortgage at 7.6% (40-year): $1,996Technically, it lowers the monthly, but not by much once factoring in the rate adjustment.

Additionally, since my parents are nearing the retirement age, I'd like to prioritize low-debt, high-cashflow deals.

Principal balance currently at 314kProperty Details: It's essentially a "2-in-1" property, with the main unit rented out for $1,900/month and an attached ADU bringing in an additional $1,200/month.

We have not disabled ours or converted to gas, but Tenant must sign a Fireplace Addendum stating if they use it, we require a higher renter's liability policy with us as additional insured, rules on wood, storage, use, safety, they pay for yearly professional cleaning each year they are there, etc.  

Since the payment was deposited into your account on 1/6/2025, it would typically be considered income for 2025, even though the tenant paid it on 12/31/2024.However, if you use cash-basis accounting (which most landlords do), the key factor is when you physically receive the money, not when it was sent or owed.

ADUs can significantly enhance your property's value by adding living space that can be used for rental income or as additional living quarters for family members.The increase in value from an ADU can vary widely depending on several factors such as the size, quality, and functionality of the ADU, as well as its integration with the main property.

Additionally, I really want to dive into the property management realm and am passionate about connecting and assisting other Veterans and Active Duty. 

Additionally, how can I estimate the total cost of construction and figure out whether the cost of land is worth it?

I'm not in that market so I can't speak specifically to it, but to me the deciding factor would be what the surrounding units and area has.