Welcome to bullethose ktwm,
It was nice seeing you at the match yesterday and I have to take my hat off to you for showing up to your first subgun match ever with a prototype in 22WMR. That's a nice looking gun and it sounds wonderful with those small bursts.
I think all your questions were answered yesterday but for the record.
Yes I think you you can use a laser at our monthly matches but I don't think it'll help you. I know the national and state level matches lasers are not allowed.
Slings are optional but come in handy from time to time.
Pistols are only mandatory during matches that have pistol targets. A good rule of thumb is to bring a pistol and 50 rounds of ammo regardless. In the event your subgun should fail you can transition to the pistol.
And bring all the spectators you like

Glad to have you on board here on the forums and I hope we get to see you out at the matches in the future. Bring some friends and remember we have a semi auto and 22lr categories in the event folks don't have full autos .
-Todd