Start with some 'dry runs' on holiday or weekends. Have a bailout plan in case you fatigue or have a mechanical failure. Don't get too hung up on which bike. If you are a novice whatever you buy will not be your last bike, so consider something used. If you are not a novice, you should already have an idea of what to ride. The fit is more important than anything else.
Most importantly ride, ride, ride. Stop delaying and start doing. You will work out the details. I am 58 and have a 24 mile each way commute which I have been doing for about 10 years. If personal and work commitments allow I do it twice a week. I see people on all sorts of bikes on my commute. They all look happier than those driving.
Above all listen to your body, it will tell you when you've had enough.