Will you have enough money to cover unexpected costs? 

If you are 90% leveraged in a market with dropping values, you’re in a tough spot if you overpay and if you don’t have sufficient reserves to account for an unexpected HVAC replacement or a tenant who stops paying/vacancy.  

Also prior to installing new cabs, run new electrical with proper GFCI circuitry and multiple adequate outlets for today's needs of numerous small, and high draw, appliances.New cabinets I strongly advise against any particle board boxes or vinyl/foil wrapped doors and drawer fronts.

You may also want to consider other private money outlets other than Hard Money. 

It's essential to have contingency plans in place for unexpected issues that may arise during the renovation process.

Things happen that have nothing to do with market factors...and you may end up needing to exit some of your investments unexpectedly sooner than you originally planned.  

Not a top earner but more of a creative outlet.

I'm curious, what are some things that have come as an unexpected benefit to folks who have a few deals under their belt?

I miscalculated the renovation costs; ran into unexpected expenses (e.g., the stormwater and sewer lines were combined so I had several sewer backups and had a lot of push-back from the municipality before I could redirect stormwater into the street); Contractors didn't show up which gives subsequent contractors with a great excuse for them to not show up (i.e., the domino effect thing).In summary, don't partner with anyone, borrow money from a HML or preferably from your uncle Billy to get you through construction and then refinance it through the VA.

Looks like you got an extra unexpected win!