So, the Thermo Control Valve (AKA bypass valve) was covered under your power train warranty, which goes to 5/years/60,000 miles. You were way past that when the problem occurred, so yeah, no further warranty coverage without an extended warranty. The price you paid for the repair wasn't out of line.
The radiator is a separate, probably related, issue. What you saw is not normal. Hopefully your mechanic simply did a sloppy/poor job refilling the system, and what you saw is a result of that. Worst case is the system is leaking from somewhere. Any puddles under the car?
Here's what I would do. Top off the tank like you planned, AND fill the radiator, then drive until the engine is fully warmed up. Run the heater as well for a bit. After it fully cools, check the reservoir fluid level. You'll probably have to add more fluid, maybe 3-4 times. Repeat the drive-cool-refill process until you you don't need to (i.e. the reservoir is at the full mark after everything has cooled). If you need to keep adding fluid day after day, and the amount you need to add each time isn't getting smaller, pay a visit to your mechanic. The coolant is leaking somewhere.
You may want to clean up those areas where there is coolant residue. That will make it easier to spot a leak.
Your pictures make it look like the radiator cap could be leaking, since there's residue everywhere. Is the seal in good shape? There's a whiteish area in the six o'clock position of your picture. Is that just a reflection?
