You can continue driving without making any changes. But:
yes.
Be wary of gusts as you pass large vehicles
merging vehicles at on ramp
Avoid speeding and hitting pedestrians or other vehicles.
As a warning at corners or if other vehicles are near you.
merge left when possible so that othe vehicles may enter safely
that depends on if you will be driving the vehicles that you will be working on if you are going to be driving them then the answer is no, if you are not going to be operating the vehicles then it should be absolutely no problem. Next time you drink just don't drive and you will not have this problem. if you still have a d.l. you should be able to drive the cars if they want to put you on their insurance.
3 ft should be all you need, just look out for doors opening into traffic.
You need to go to the DMV and identify as an interstate driver (which you should have done, even if you were driving intrastate at the time). If you were restricted to intrastate only due to age concerns, you need to get a duplicate from the DMV with the age restriction removed.
Mom should have a discussion with her auto insurance carrier. If they are not driving the vehicles regularly, say a couple times a month, most policies will allow it. But if they are driving it regularly, she needs to make sure she is protected. Father's policy may have a rider for driving other vehicles.
You should leave enough time to allow you to stop safely if the car in front comes to a sudden halt. You should be aware of your vehicles stopping capabilities and adjust the driving time accordingly.
On many vehicles, that means that the daytime driving lights are on.