1. there is no requirement for clearly visible in car. CRS 18-12.105 / 18-12-105.6
2. Illegal CRS 18-12-108.5 - it at glance is 'legal' under 18-12-108.5 (2) BUT.. legal guardian has to be in "control" of real property.. not in a store.
3. As above
4. If it is in car open or concealed it's not an offense if unloaded CRS 18-12-105.5(a) Not an offense if you carry a legal CHP CRS 18-12-105.5(d.5)
"Loaded" is defined as a round in the chamber CRS 18-12-108.5(a)
5. I wouldn't do it.
6. Could result in a brandishing charge or Criminal Mischief.
7. Yes except in Denver County and posted gov't buildings (and a few other places)
Note to # 2.. I didn't read lockbox.. you should be ok w/ a lockbox.. to possess means the prohibited person has access to the firearm or can affect it. meaning a trigger lock is not sufficient as the prohibited person or juvenile could still transfer the firearm but a lockbox with a combination or key that the PP has no access to is OK.
Take a look at CRS 18-12-108.7 too