Impossible to answer without knowing all the variables that mean "best" to you.
1915-1916 is a best estimate
1910
You need the services of a gunmsith.
150.00
Centerfire
In the owner's manual
Not in any reference I have seen
10-90 usd
25-50
Proofhouse.com has Colt sn tables.
Less than 100 USD
Maybe 100 or so