-"commercial" local/regional tiny house builders will offer some financing option or another, find someone local in your price bracket and work with their financing-park models can be financed through dealers/(etc), and small ~400 or 600 sq ft singlewides, although getting spendy, perhaps, could look attractive once you factor in the negative of anything smaller being tough or impossible to conventionally loan down the line.

What type of lending options are out there to get additional 50k and refinance home?

I would price out both Heloc and cash out refinance side by side to look at best options.

Note that you typically have two years from the date you paid the tax or three years from the date you filed the original return (whichever is later) to submit an amended return.FORM 3115This is a specialized IRS form that is used to request permission to change an accounting method.

As @Jacob Sherman mentioned, lenders prefer and typically require to be the sole debt on a project (mortgage).

DSCR loans are typically not reported to credit agencies. 

Define your long-term goals carefully, determine your ideal outcome, plan ahead, and refrain from spending any money until you have thoroughly evaluated all your options.

Assuming it is an REO, they are typically offered with title insurance.

A 1031 exchange can be a great tool, but it’s typically used to defer capital gains taxes when you’re selling one investment property to buy another.

This cap typically remains in effect unless there is a "change in ownership or control" or a qualifying improvement to the property, among other exceptions.