There is very little reason to go with a THR other than having some other complication like AVN, or something beyond the standard OA degeneration of the hip. Although that doesn't exclude HR right out of the gates. It's best to discuss with an experience HR surgeon.
I think there has been a bit of a mini exodus for the partially experienced HR surgeons. It's a more involved surgery and it requires more experience and so with a little bad press (unfounded, BTW), the less experienced leave HR and stick with THRs.
My scar is about 6 inches long. The length of the scar has to partly to do with size of the patient, but also has to do with how much room the surgeon needs to do the work. HR scars theoretically should be longer than THR scars, because you have to manipulate tools, drills, grinders, templates,... in an around a non-sawed off femur. I don't think they gain much room when they dislocate, also. Anyway, the more room the easier it is to work and the more likely the surgeon will get a good fit/angle, product. I should say that there are some really experienced surgeons who are known for shorter scars and they have excellent results.
Running with HR - popular topic. I get the feeling (from reading so many posts here) that the less experienced surgeons are more likely to be the ones that recommend no running with a HR. None of the common name surgeons tell you no running other than during the 6 to 12 month recovery period. I suppose there could be some unusual circumstances, but again, like Hern and Imgetin said, the point of HR is so you can run.
I agree with what the others said on knees and staying in shape.
Welcome and ask the surgeon lots of questions, and consider second or third opinions.