I have a wife and you think that might be helpful with things like sewing... not so much here. She was banned from the sewing machines in gr 7 or 8 home ec because she kept breaking needles
after 6 needles, she had her priviledges revoked!
She's VERY enthusiastic about the diapers I make though and she does let me know when she likes or dislikes a material and she gives me good suggestions for what does and doesn't work which have all made my diapers better.
She also keeps me fed. I'd starve or have scurvy if it weren't for her!
so, that's way off topic.
To get back on topic... I use chalk on dark colours and marker on light colours. I usually use something permenant (i hadn't thought of crayolas being washable! what a GREAT idea!) and cut inside or turn and topstitch.
when you're sewing the curves, just feed the material into the machine the way you want it to go (move the fabric around so the machine takes it in as if it were going in straight.) it won't take you long to get it right.
You have to do the same with a serger. In fact, I find things trickier with a serger than my sewing machine, but I've had my machine for 8 yrs now and the serger is borrowed from my neighbour.