How does the Hardware Expert aced skill work, especially with drills

No you cannot see the map during the game. It gives you information about the mission before starting the game. The information is quite useful, for example, people carrying keys you can take and alternate paths.

You need to buy the assets you want each time you enter the mission lobby. They will only last for one attempt and are lost when you start the mission.

Reloading adds more ammo to your active clip. The game uses an ammo pool, rather than a clip based system, so there is no downside to reloading more often than necessary.

I think you're asking this because of the numbers on the HUD.

Here, the number on the right is your current total ammunition, not the ammunition you have left after your current clip, and the number on the left is the ammo left in your current clip. Shooting depletes ammunition from both pools. Once you reload, the right number will not go down, it will simply fill the clip, making the left number show full clip again.

Now, I shot 5 times after the first image without reloading.

And this was taken after reloading:

This doesn't seem to be the case for all weapons, however, but it is the case for normal shooting weapons. The OVE9000 Saw, for example, has some sort of durability as the left number, and the amount of blades left as the right number on the HUD.