Actually, the natural ruler of the 5th is Venus.
Stellium is when there's 3 or more planets in the same sign. Yes, you do have a Capricorn stellium since you have 5 planets in Capricorn.
No, just because you have a bunch of planets in the 5th doesn't mean that you have Leo traits. The Capricorn planets in the 5th house will express itself through 5th house matters.