This is because you're spreading the income out over many years rather than making a large contribution in a single year, which may put you in a higher marginal bracket.The part with a traditional 401(k) that doesn't get taxed is the time the money "sits" in the account.

These loans are strictly for investment properties where the property is owned and operated for business purpose and rented out for income.

It's important to reassess the income for requalification.

I am in search of an efficient system  to track my rental properties regarding income and expenses to make it easy for my accountant at tax time.

It reflects the average rental income per booked night, including nightly rates and additional fees like cleaning charges, pet fees, etc.

Do the math, if they will not reduce, then move on, it's only a thousand bux.

Is it recommended to have it furnished to reduce the amount of moving damage it can cause?

If they decline to share, that is a red flag which would warrant walking away or at a minimum substantially reducing the price instead and basing the offer on your own numbers validated by third parties.

two income streams for one sfh.

Because if you pay rent to yourself as an expense of the LLC then you have rental income on you personally.