The key here is to know what's in your HOA documents.Generally what happens in a situation like this is that you would make a claim on your insurance and then they would subrogate it to the responsible party (either the HOA or the other unit owner), so I'm surprised that your insurance company is giving you the run around.Make sure you've got a written statement from YOUR plumber indicating where the plumbing fault came from and, before you patch the drywall, get the HOAs plumber in to look as well (if they have one).  

I will be doing most of the rehab myself but I will need a reputable HVAC mechanic and painter.

This would also hold true for plumbers, electricians and roofers.

I am starting to build a quick-list of trusted/recommended plumbers, electricians, etc. in the Des Moines area that I can call in the event of an emergency.

If none has been done then you will need to have a septic company come and spec one out or a plumber who can do city connections.

You could potentially team up with a reputable local wholesaler/company and allow them to perform ALL of the work and share the spread with you.

@Ali Boone I would be very interested to get your recommendation / feedback on reputable turnkey companies. 

@Sam MillerWith a relatively small number of reputable providers across the country, choosing the right firm to work with usually involves going outside one's local area. 

Looking specifically for a plumber and an electrician. 

Does anyone know of a reputable and experienced operator in the Los Angeles area that might be able to help?