I would not worry about a 12 year old roof if the previous job was completed professionally with architectural shingles (which is what I would expect). 

Should I hire a roofer, I can put shingles on"?"

Understand not much  can be done about the weather , but contractor is recommending an upgraded shingle : TruDefinition™ Duration STORM™ ImpactResistant Shingles with WeatherGuard®  Technology To use for this replacement -  Has anyone used this shingle and offer any recommendations on whether it is worth it or not , and what other measures are you taking against hail storm damage 

Many of them also have weight limits, so if you are filling with concrete or roofing shingles you may have to pay extra. 

Even then, I still occasionally made mistakes; for example, no one told me it costs and extra $3,000 to redo a shake shingle roof. 

I had to clean up job sites(harder than it sounds), pick up shingles,break concrete up, and so on....very hard work and I live in FL.

An architectural shingle job up here would cost at least $15K.  

When an HOA covers the exterior (driveway, lawn, shingles/roof, siding...) and I would be responsible for windows and interior... how would you calculate CapEx/what percent would you use?

Purchase price: $39,000 Cash invested: $100,000 Sale price: $190,000 Our most recent flip in Shingle Springs, CA that we took down to the studs and built a luxury dream home in its place.

Have a SF rental property in   Louisiana,  and after receiving an initial  all clear from the PM after the latest hurricane, Tenant came back and said roof is leaking and some shingles are gone.