Hi there -- welcome to the boards! I don't have a specific answer to your questions about recovering from a knee replacement, but I had several hip arthroscopies and a back surgery in the last few years. I am a little bit younger, so expected to recover more quickly. I still have rough back days (9 months post-op) and bad hip days (15 months post-op). I'm not sure whether the pain you describe is just from being a little sore or something else.
Be careful not to do too much; if you have an overexertion injury, you will probably face a period of total inactivity. Most athletes train by using a ten percent guideline. Find an amount of exercise that doesn't cause pain, then add ten percent per week.