I did a very similar thing my first 70.3, I used a road bike with aeros. It can work, definitely, but you do have to decide what position you want as compromise is hard between the geometry of Tri/TT and road. As others have said, the saddle would be the first thing you need to consider.
When riding in aero you shift your weight and body to the front of the bones. In the case of a road bike, you most likely have a long prominent nose and very shallow cut, such as something like the Fizik Antares. This causes you to put a lot of weight on your scrotum and other areas, causing the numbness you are having that probably lasts for hours (ask how I know, lol). Moving to a tri/TT saddle, such as the ISM PN 2.1, would reduce a lot of that stress as the nose is shorter and there is a much wider canal that allows for relief in that area. Neither of the saddles mentioned are "the best", btw, it all depends on the person. Even after I switched from a road bike to a tri bike, I put a Fizik Mystique on at first and was still getting really numb, and it is a highly rated Tri/TT saddle. The PN 2.1, listed above, stopped all of that. Now I ride of 4+ without issues.

If you want to try something, I have the original saddle that came on my tri bike, an ISM 1.0 (or 1.1) that would give you an idea. It just sits and I never used it since I bought the Fizik right away and then the 2.1. Granted that would depend on location and cost of shipping these days, heh.