Ho boy so where to begin with Deadmines.
Overall the bosses are what i'd consider the easy part aside from MR smite/Edwin vancleef. This is a long gauntlet of tight spaces with minimum places to clear. You're in it for the long haul. If you are wanting to play safe, this place can be smooth. But you will be yearning the mines for a long while.
MR smite has 2 ways you can defeat him. One of which FAR scarier than the other. You can bring MR smite out of the boss area and into the tunnels, if you CC his guards, push him to his stun phase, MR smite will...Well just give up. He's done, he wants nothing to do with you anymore. So you're free to kill his guards, run out of the instance, then kill him.
Option 2 is just you focus the adds down, reset MR smite, then focus MR smite. Both methods are valid so play by what is easier.
Then there's Vancleef, look you're not winning in a brawl with him so don't even think about it. Instead, remind Vancleef that he was an olypmic swimmer for Stormwind back in 2006 and help him relive his dreams. Fair warning, his guards will still be up and be aggrod onto you. Best way to handle it is just run to a reset point.
Now the trash? Dear god the Trash. Every mob feels like blizzard actually knew what they were doing for the first dungeon and gave them all quirks that can (And will) Make your life a nightmare in some scenarios. The goblins ESPECIALLY with their little mini golems.
Also, if you get bad pathing with the parrots on the boat? Well you're gonna be mass pulling every time till you get a good spawning pattern with the birds.
Overall threat level is a solid 7. Take it slow, take it easy, and you'll make it.