One of my favorite cars was a 59 Belair. The nonpower steering was just fine due to the large steering wheel, keep the front end greased good all the time. The stock, non power brakes worked very good and I never felt stopping was any safety issue. I would say that seat belts are a must in any car and wouldn't hesitate to install them. Other than that, where do you stop? Are you going to put airbags in your vintage car? Re-engineer it to have better crumple zones? Disc brakes are fine, I have them on my 29 RPU but more because they are easier and cheaper to install than drums when you are building from scratch. I don't think it would be hard to upgrade to discs. If you plan to drive in the metro, they would be better for sure. Everyone has their own personal preferences but the car doesn't have to be a canyon bender to enjoy it and drive it daily. Sure it might not handle the wet, metro or canyon roads as well but you learn to adjust your driving style to what you are driving, same as if you were towing a trailer or driving a 4x4 instead of a sports car. Common sense has to prevail no matter what you are driving.
Once you get the car on the road, you may come to love the feel of it. Sure some adjustment to driving style will probably be needed but just learn to slow down a little and enjoy the ride.