Not an expert on baby gear, but I do think these are two separate things. A convertible car seat is one that will grow with baby, work frontward and backward and typically stays in the car. An infant car seat is the kind that you can take out of the car and attach to a stroller (chicco key fit). Both will work with newborns (depending on size requirements of the particular brand) but only the infant one will come out of the car.

For strollers, you mentioned waiting until babe was big enough to jog with you and that's the main point. The infant car seat is specifically designed to be convenient for parents when babe is tiny and getting in and out of the car seat is particularly difficult. A babe that small probably shouldn't be jogging anyway, which is why strollers have size requirements. The only strollers appropriate for newborns have a bassinet setting, where you can lay the back completely flat. Even if you do have an infant carseat that attaches to a stroller, it is not recommended to keep babe in the car seat for long or let them sleep in there. Of course, people do it all the time, that's just the recommendation.

I'm not planning to use a stroller until babe is bigger. Instead, I will baby wear. I'm also planning to use a convertible carseat that stays in the car. This is my preference to avoid keeping babe in carseat longer than necessary.

I would suggest finding a good jogging stroller that will work for a long time, then follow the size guidelines on that stroller to determine what other gear you need for the earlier days. This might mean buying two car seats and/or two strollers. Hope that helps!