First of all, welcome to the server!
As for the weapon license system, you can obtain it inside the Police Department for $500k once you reach level 5. The fee to obtain the license keeps on increasing up to $8m when it's revoked. Also there is a cool-down period(1 week for the 1st revoke and 2 weeks afterwards) before you can obtain the license again.
And regarding the inactivity rule, you need to have played at least 4 hours in the past 2 weeks to avoid getting your properties removed(applies only for houses and businesses).
Click here for more details regarding the inactivity rule