I can't decide between exploring a 203K loan or getting into flipping mobile homes.

Additionally I've also purchased a shed at my own home in the past year with which to store these tools and materials which I believe is also a legitimate deduction.

You should consider learning about house hacking, BRRRR (Buy, Rehab, Rent, Refinance, and Repeat) and group home investing, I feel.

I am considering adding a small studio (attached junior adu) of about 264 sq feet to my home in San Jose. 

I am debating if I should buy a decently priced home in Florida using a mortgage, rent it out as soon as possible, and have a tenant(s) pay down my mortgage until I am ready to move in and have the mortgage either paid down or nearly paid down.

The purchase price of this three bedroom two bath 2100 square foot home is $230,000.

I owned a home in queens, so house hacking is not an option for me. 

The opportunity arises after a family member, who has a clean title and owns the home outright, let the property go down the drain.

If the home is uninhabitable which it is, renters insurance could cover other housing - similar issue if it was a flood or fire damage.

Regarding downsides, or perhaps good barriers to entry, saturation is pretty strong, good help is quite hard to come by, inventory has been hovering around 25 or so homes for a while (most of which are not STR material), and much of the recent cabin listings have been grossly overpriced.