From a design perspective, I think you need to work on a more cohesive look throughout and tone down some of the colors you have going on in the living room/kitchen.

As far as colors to pick, what floors, and what’s trendy looking. 

Do you have a ducted heating system, is it a system where all components have failed or just the seperate AC unit.

Certainly replacing a furnace and/or a water heater would require a permit as well as running a new or replacing a duct run.

My advice for you (and my future self) so far is:- be very detailed about underwriting your deal- add at least 30% to what you think your rehab will cost (even if this figure came from a GC)- have a really detailed design concept before work starts (including fixtures/trim/color scheme/etc)- check with your city/township's building department and see what permits you need up front- have more than one exit strategy- add a few weeks/months to your projected timeline- purchase cash if at all possible- build relationships, take notes, and learn lessons along the way- have funGood luck! 

Some people are allergic to rabbit hair so I would need to get the air ducts and entire house deep cleaned if the tenant moves out. 

., I have heard of painting walls etc with Kilz and running an ionizer and stripping the popcorn ceiling but what about the AC ducts?

If you do not put in a 2nd HVAC system, pay attention to the return ducts.

Paint colors, flooring, price per sqft labour and materials, etc...

They also come in colors (by order).