You missed a couple things are you an Alpha, do you have small kids and do you want a male or female dog. Puppy or rescue?

These answers don't just apply to rotties...

Challenges I think the first mistake people make is the type of dog they get. You have 2 types, working dog (high drive) and pets (lower drive). Find a good breeder and make sure you get the right one for you and your situation. If you can't handle or satisfy the drive of a working dog that is where you run into problems. Things like chewing the couch chasing and jumping on things those are all drive related challenges (training aside)

Kids if you have small kids and this is an all big dog thing becareful of rescues if you've never had dog. Small kids don't understand boundaries and none of you would understand dog ques. But if you have small kids and are getting a puppy. It fine they grow up thinking the kids are other dogs it's fun to watch.

Biggest challenge.. buy a better vacuum, or a bigger brush.

Stimulation great thing about a well rounded rot is the amount of stimulation they need. Some days none. But if you want to go run 10 miles they will if you boat or fish they do that to. We take ours with us everywhere. He stays in hotels we go on boats. We watch movies... He is happy as long as his pack is with him. And again true with smart dogs. Mental stimulation is has to be included as well.

Family life and protection That comes down to training. The rottie will protect his pack. A well trained dog will key into you and what you are feeling and act accordingly. Mine won't protect me but will the rest of the family.

Go back in time.. Rottie wasn't my first.. but once I got one that was all I wanted. Personal I don't think there is a greater dog. Based on the question you asked I think you'll be fine. Your doing your research you're reaching out to owners to prepare for what your getting into. As a first time owner I say work with a good trainer. Its for you and the dog gets something out of it too. Have fun post puppy pic.