One designer is offering a flat fee of $3k for 3 months of consultation.

In effect, you need someone to design the change and figure out if steel is needed vs wood framing.

It is almost like it was designed for investors.

If you're wanting someone that's going to play an active role in guiding your real estate investing, you might be looking for awhile...If you don't already have an advisor in mind, I'd suggest you start by looking for a fee-only advisor with a CFP designation ... you can search for one in your area here. 

My wife (realtor) and I will be handing architect/interior design and the sale of the property. 

Mold is ubiquitous in the environment and your immune system is designed to deal with exposure.

That said, we're both motivated and my partner particularly has a knack for interior design, so we're not averse to a property improvement play.Is house hacking a realistic option for us?

For me, I picked my end goal and designed my plan around that.  

Sounds like they do want to retain the separate property designation.

When these new investors explode here, usually with something like an SFR that's 40-60 years old, they say nothing about roof design, basement wall construction, beam placement, site slope, drain extensions, none of the things they should obviously be thinking about in buy a property they intend to hold 20+ years.