Oil prime, then spray with a good quality oil paint for a harder finish.

It is copper based and one quart will treat 40,000 gallons so just dilute it in any old spray bottle about 50/50 with water and spray the affected areas, and let it dry.

And there was a PEX joint that had no clamp, so that was spraying - but it was close to the water shut-off valve, so they quickly shut off (otherwise the ceiling leak would have been more damaging).

Typically batt insul is used in this situation but rigid could be used.2b) Spray foam insulation to the wood deck with a new lower drywall ceiling.

. $4 per spray can and needed about 4.

I would spray foam every joist space with closed cell foam.  

Spray it on the stain, let it work for a minute or so, and then wipe up with paper towels or a rag you don't care about. 

I would get several cans of the low expand foam for doors and windows (brand name of 'Great Stuff' is just one of them) and spray foam complete entire window bay from top to bottom.If that stays dry thru a couple cold or wet spells drywall over this area with either drywall rated as moisture proof,,,mold resistant,,, or even use cement board tile backer(that should NOT harbor mold)...Paint to match

Get someone to spray it - it will look new.

Why pay for lawn care for $100 per month when you can do decorative rock or other xeriscape designs and hire some neighbor kid to spray weeds once a month?