We were novice owners of a rescue dog that was described as anxious and fearful. We didn't even know the word reactive! But it quickly became obvious that she is very reactive, particularly of other dogs, and particularly on lead. 4 years on, and despite behaviourists and training classes galore, she isn't a lot better. She's the love of my life and I wouldn't go back and change the decision even if I could, but it is a lot of hard work, it restricts your life in ways you can't even imagine, and it can be very lonely and upsetting.
As an example:
Can't be left with family or friends who are not dog experienced.
Forget allowing the kids to hold the lead on a walk, that ain't happening
Can't go to day care or kennels, can only be left with an experienced solo sitter, and they are not easy to find!
DH and I both have to WFH as much as possible as a solo sitter daily is incredibly expensive and pretty much impossible to find
You can forget lovely lazy afternoons in a dog friendly pub - there will be other dogs!
Ditto days out at the beach / busy parks etc
Every walk is fraught with 'danger' - you become expert at finding remote out of the way places no-one else goes to. Most dog owners enjoy dog walks - you won't unless you're in the middle of nowhere!
You will have a LOT of run-ins with other dog owners who allow their off lead dogs to run up to yours shouting 'don't worry mine is friendly'. If you're not assertive by nature you will have to learn to be very quickly!
Using secure fields for exercise can get expensive when you're doing it a couple of times a week
We don't have children, and have been able to adapt our lives to keep her within her comfort zone most of the time, but it hasn't been at all how I imagined having a dog would be. You have to be very, very committed. Mine may be a bit of an extreme case but I know several other people with very similar (or worse) issues so I think you have to be prepared that this is what it could be like, and accept that once you take on the dog, you're 100% committed. Taking it on with a 'we'll see what happens' attitude and hoping for the best would be incredibly naive in my view, and likely end up with the poor dog back in rescue with even more issues.