If you're able to subdivide the lot into four new R1 lots, then each R1 lot can handle a duplex and two exterior ADUs -- ie, two duplexes.

While considering raising the rent to reflect the market rate and adding an additional $100 for utilities, I find it challenging as we have built a positive relationship with the current tenants.As for our Studio (STR), I would appreciate any suggestions on ways to optimize the income potential of this space.

Curious to know how you would handle this situation.

This would combine LTV, combine your cash-flow, and give you one mortgage payment for all properties within that portfolio. the benefit here is you'll likely see better rates, and you'll be able to leverage one properties good equity combined with another properties strong cash-flow.... but the down-side is if you want to take one out of that portfolio to sell or refi, "partial release" can be a challenge. also, most of these are not 30 year fixed, they're likely 5 year terms/ 7 year terms/ 10 year terms on a 30 year amortization... still stretches payments out, but you have to do something ab it again once the term expires. 

This can make them challenging for house hacking strategies.

Challenges?

We are rapidly growing and are handling the scaling well (which should be the most difficult part).

The challenge with fire damaged properties is that there is more than meets the eye.

The vast majority of people I've called don't immediately fly off the handle. 

We share our wins, discuss challenges, and celebrate each other's successes.