When you transplant a seedling directly from a solo cup to a 5-gal. pot you are going to enjoy a couple of wasted weeks. Plants spend most of their initial energy growing roots to fill the pot. Until the roots reach the pot there will be little growth above ground. That's why we usually TP from a solo cup into a small pot. The roots will reach the pot a lot sooner and start that important veg state.
Good luck, BigSteve.