My first bike was a 750. Not ideal for a first bike, but can be managed.
First, no passengers. If this is your first bike, you don’t have the experience. When you’re riding you are very much part of that bike, everything about how you move and how you hold yourself affects the bike. By extension, that includes your passenger. Get comfortable on the bike, learn how to control it, once you’ve been on it for a while (normal suggestion I hear is one year), then you can carry a passenger.
Second, at anything less than highway speeds even a 250 has plenty of power to get up and move out of the way. You don’t need to worry about outrunning anybody. That’s the wrong solution. The right solution is to remove yourself from where the trouble is, and that’s usually going to be more about maneuverability than speed. When the SUV pulls out of the driveway without looking, speed won’t save you, but being able to stop quickly or swerve to a safe path will. Likewise, you can tuck into small protected spaces when you find yourself about to be run down by somebody coming from behind. I’ve been hit in both situations in my car, and in both cases a motorcycle would have gotten me out of them safely.
Know your power band, know how to use the friction zone, and know how to do your slow speed maneuvers. Those are the physical skills that will keep you alive.
I also strongly recommend the Motorcycle Safety Foundation’s Basic Rider Course. They spend two days teaching you about all of the low speed and evasive maneuvers, all things that will help you stay alive on the road. They’ll also tell you about some mental skills that, when applied, will do even more to keep you alive.