I moved two Nucs yesterday to unite them with Q- colonies. Not a complex process or one that should be overthought but I accept that it is daunting the first time you transport bees.
Nuc 1, Home apiary. Entrance closed with a piece of foam rubber pressed into the entrance with my hive tool. Feeder removed and piece of slate slid over the feed hole in one move. Time: 10:00am. Strap placed around nuc, running over the piece of slate and Nuc carried to car. No bee suit needed. Drive to out apiary - no bee suit. Nuc 2, out apiary, a simple process of flipping over a piece of floor mesh that is screwed to the nuc box and allows you to close the bees in but also gives a little ventilation. Strap around the nuc. This was done right before I lifted the Nuc and carried it to the car. Time: 11:00am. Bee suit and gloves on as i needed to take a quick look into another stock of bees. Before the nucs were set into the car, I lifted them up to check for "loose bees". The second nuc had five or six and they were brushed off before the nuc went into the car.
Both nucs have spring clips holding the floor and box together. With a strap around them, they are only going to come apart in a catastrophic event....
If you are concerned that your hive isnt secure or that there are a few loose bees clinging to your hive, wrap it in an old bed sheet. I have a few in one of my storage cupboards for this purpose but they tend to get more use from people collecting nucs from me than from me directly.
With regard to ventilation, if you have a long car journey to make, make sure the bees are well ventilated and its probably not a good idea to crank the heat up to full in the car. All my nucs have mesh vents in the floors and my full hives have mesh floors and so they are ok for the distances I expect to move them.
If you spot bees flying in the car when you are driving, just put the car windows down - air flow will tend to push the bees to the back of the car. I would be concerned that if you wear your veil you will be at greater risk of failing to see a road hazard than being at risk of being stung by one of the bees in transit. Above all, keep calm and carry on!
PS - should have added that it is my practice to align hives so that the frames run in the direction of travel - even though frames may be propolised together, this orientation reduces "swing" when moving the hive.