That's great! It's nice to know someone appreciates handmade knitted socks.
If you're not sure you have enough yarn, do you have something that would coordinate and make the heels and toes a different color? If you're doing toe-up, you can make the cuff whatever length you have enough yarn for. This might be a good reason for an afterthought heel, you can decide later if you want a different yarn for the heel.
I should never overestimate my basic arithmetic skills.