Note that the diagram doesn't consider tax implications—that's another important factor you'll need to include in your decision.

Aim for $500/mo min and even that won't allow you to tap into unless that's after cap ex, management, vacancy is factored in.

Ignore the $1,250 per month because that's your cost of housing, if you didn't pay that on the home you'd have paid that in rent so that's a non factor. 

It's just not the reality.I don't know your wife's income so it's hard to know what you need to replace in order to let her retire but if you think you'll get her retired in the next year or 2....you will have a 99% chance of being let down.Becoming financially free, or not needing a 2 income household comes down to 2 simple factors.

Meanwhile, the sellers who are most likely to offer creative financing are normally the owners of  real estate that have issues.....condition.....low barrier/over supply market......or perhaps pricing issue, and one of these factors is why its not marketable in a arms length transaction and why creative financing would be accepted.

Also, factor in potential interest rate changes if the HELOC isn’t fixed.

The major factor to standing out in any market is design.

Will depend on several factors like the type of property, type of tenants, your risk tolerance, other assets you own, your estate planning, laws where the property is located, etc.

Most of the designers I have have sort of a baseline price i.e $2.50/per foot but it can go up or down on other factors

That is $19,200 annual profit so you would be -$3,200 in 1 year with no factoring of breakage and maintenance.