This is not gonna happen. We discussed that in another sub 3 hour thread as well. You need to have quite a level of speed and endurance already before you start to tackle sub 3 hours.
Most likely you will be very injured in fall, if you try this.
First you need to get into running slowly, 3-4 times a week and then you can eye a Half Marathon in fall and see how that goes. I would even not put the Marathon in your goal list before 2023.
Reality check: You are 48, didn't run forever, overweight for a runner.
You need to get you body in shape before you even consider doing a Marathon.
The sub 3 hour goal while not impossible for some, it is probably quite unrealistic. Now or in 2023.