Hello Phil, and yes, welcome to a life-changing forum! Your path has many similarities to my own and what I have read from other others! To help answer your questions:
Intensity. Without a doubt, this is a challenging attempt to return to normal. I had my left hip replaced 6.5 years ago and my right hip replaced a year ago. With the left hip, trying to do faster repetitions, almost always resulted in strains and hamstring pulls, Even when doing relatively slower work in the form of 5K. Also have had this experience with my newer right side… I’ve had Hamstring pulls and tweaks and pulls in my first several months. Knock on wood, I have had not any of these issues in the last Two months and my intuition tells me that I am over this phase. That said, I am very cautious and how I approach speed work. Part of that would be if I did not have prosthetic joints at my age (55); Certainly makes sense given to prosthetics now
Feeling. Do your hips feel 100% natural? This is hard to say… As a lifetime Athlete and having shifted into endurance sports in my upper 20s, by my upper 30s, I would say that my joints were “tightening“ and I probably looked a bit “stiff” compared to other members of the active adult population. By my upper 40s, I was needing joint replacement. So in today’s terms, I probably feel about what I did in my upper 30s and that is I am stiff but not in pain… Hope that makes sense. I don’t feel like I run as smooth or naturally as I did in my upper 20s.
Balance. Without question, a newly implanted prosthetic on one side Will likely cause forms of compensation on the other. I don’t think there is any way around that But to gradually build and adapt. Resistance, conditioning, and overload takes 6 to 12 months in my experience, to get anywhere near to where you were pre-surgery.
Hope this helps and best wishes, Phil!