Done! Three pairs of pants with extra-long legs.
Thanks for all the advice and feedback! It was all very helpful. I added about 5" to the longest length on the pattern. Had to redraw the calf pattern line because the two pieces didn't match. It was strange to use a paper pattern instead of a tissue-paper pattern, but it is very durable. I reused it three times and it's still in good shape.
It's a nice, simple pattern and the gusset wasn't hard to insert - you just do one side at a time. The seam allowances are really narrow, which I liked because I hate trimming seams. However, I should not have clipped the notches in the seam allowance; I should have chalked them because the clipped notches made the seams hard to sew/uneven, especially the center back seam with the double notch. I made a note on the pattern to remind myself next time.
Tip: When it comes time to fold the legs to create the inseams, start pinning from the hem to the gusset. It made matching up the pieces easy-peasy. I tried it the other way and sure enough, I mismatched the pieces and had to pull all the pins out and start over.
The front fit was a little bunchy, so I took it in a bit to make it look flatter/nicer. Have a little fabric left over, so I might make the shirt pattern with some colored lycra scraps I have in my stores, just to use everything up.
The kids think the bottoms will stretch over the boots, but I'm not too sure -- we'll find out soon enough. I figure if they're too narrow, I'll open up the seam and insert a panel to widen the bottom.
Thanks again!