Hey noblezada,
I use a wireless when I perform, so I stand up, walk around, solo on tables, and sometimes on a bar, lol. I definitely use a strap, and I usually have the locks on it. I used to walk from room to room when I practiced, so I've always been more comfortable standing.

You have to do what's right for you though, try some different things like standing, and sitting in chairs, see what feels most comfortable to you. Where your guitar hangs can make a difference also, too low can hurt your back, and leg pain or numbness can be caused by back problems. The reason I wanted you to know that, is because you said it felt like a pinched nerve or something. I've been through that, and it was, and is a back problem.

Some guys also lean on the guitar when practicing, this can push it into your leg. Doing that for a long period of time, can make a difference in your circulation.

You said you use correct posture, so you probably just have to let your body catch up with your practice schedule.

JD