Don't stress it. You will be unable to be promoted to LC untill you have spent all available skill points. If you don't spend them all youll just be at Lt-11, and after you buy your skills you'll be LC-1. I guess this system is in place to ensure you don't save up and purchase all higher tier skills, and leave the lower ones blank.
Yeah, you have to spend all those points anyway to get promoted so don't worry too much about it. You can play around with a skill calculator like http://sto-builder.binarybit.ch/ to test out various builds.
So, I'm not so secretly concerned I'm leveling wrong. I've just been getting skill points and spending them. I've maxed out four lieutenant abilities and am halfway through maxing out a fifth.
Given that there is a skill point maximum, should I be stockpiling skill points until I hit lieutenant commander?
Nope, keep spending em because if you don't spend em... you actually won't make lt. commander.
There is a skillcap futher along the road, but you need to spend skill points to reach the next rank. So don't worry about that, but higher up you will have to pick certain skills/aspect you want to progress in and excel at.