I'm planning on getting into finish carpentry so I'm not sure how to accommodate for 12' & 16' baseboards. How do you guys usually carry them?
If you are able to, get an account set up with a couple of millwork places around you.
No matter how I've run the #'s, it's almost always been cheaper to have stuff delivered.
The only times where it hasn't been is when you need a stick NOW, for whatever reason, i.e. running short a stick for finishing up a job, you under-estimated, more waste than you accounted for, etc.
With a rack for the truck/trailer you're fine...but I would recommend having materials delivered if you've got the time.
If you're a one-man show, small material deliveries may not be cost-effective due to you having to spend time meeting the delivery guys, that's fine too.