Very poor description to base a value on. Broad range 300-800 USD.
Yes
You will have to call Colt with the serial number.
500-800 depending on what "very good" turns out to be.
No way to answer without the entire serial number. You can call Colt and they will tell you.
The Colt AR-15 is a sporter rifle
100-1000 usd
@ 40 inches.
Contact Colt, on line aucitons.
Proofhouse.com has Colt sn data. If not there, call Colt and they will tell you.
600-1200
100-1000 depending on specifics
Blue Book of Gun Values