So, what we have here is this big curve. You have the option of pinning carefully all along the curve and stitching. I find that can lead to puckers. What I do is just lay the beginning corners perpendicular to each other for the first stitch. Then I just carefully align the corresponding edges all the way along the curve with my thumb and forefinger while continuing to stitch. Works like a charm.
Before I stitched the two pieces of each pant leg together, I stitched some ric rac ("rick rack"? "ricque racque"?) along the seam allowance of the outer pant leg piece. This is then tucked into the seam for a little extra detail.
I have topstitched all the seams with a nice thick bright green topstitching thread.
Now, it is time for stitching the fronts to the backs at the outseam. For this second pant leg, I removed the initial basting stitches and put in new ones, so that I could ease that middle section to match the back pant leg just perfectly. I got lucky on the first pant leg: My initial gathering happened to fit just fine.
I have pressed the finished outseam toward the back and topstitched.
Now comes the time to lay the inseam edges right sides together and stitch, giving me the completed pant leg. Topstitching the inseam can be done a couple of ways: You may either work the pant leg over the free arm, but that will only get you about half way up the pant leg. In this instance, you'd flip the pant leg around and topstitch over the free arm from the other direction until you meet the initial top stitching line.
Or, you may topstitch this inseam in one fell swoop by scrunching the pant leg behind the presser foot, sort of turning the stitched part of the pant leg inside out as you go. You do not place the pant leg over the free arm, but stitch that little bit that you can. And then scrunch that stitched part behind the presser foot. Stitch-stitch-stitch/scrunch/stitch-stitch-stitch/scrunch/stitch-stitch... Eventually, you'll make it all the way up the pant leg.