Considering that you're both designers, an ugly house(with good bones!)

My market is full of older properties whose bones are still solid but haven't seen an update in decades; these are ripe for BRRRing. 

There needs to be a lot of meat on the bone for that arrangement.You should know why the seller wants a cash offer.

We own old houses, if there is a backup and it isn't caused by the tenant doing something like flushing chicken bones (true story) then we will cut them some slack and teach them to avoid it happening again. 

(B) One detached, new construction, accessory dwelling unit that does not exceed four-foot side and rear yard setbacks for a lot with a proposed or existing single-family dwelling.

4.5% is low, for that cap rate you would want this to be in the absolute best of areas, and even then in many parts of the country that is not enough meat on the bone.

If you have a proof of concept and there is enough meat on the bone this could work although that would be very generous of you to exchange equity for working capital if they are not bringing anything else to the table.

When one buys a high priced distressed property, fixes and flips, there isn't much meat left on the bone. 

@Robert Burris Not enough meat on the bone for me.

.- Check window trim for wood rot (I have a constant bone to pick with window replacement companies that offer window wrapping for older homes, completely hiding existing trim as it degrades further and lets in more cold air!)