First guide. I'll be short and straight to the point.
Hecarim is squishy early till he got trinity so i give him tanky rumes. I put dmg quints cause the lack of ''q'' build up till late.
Some damage and damage return for early jungle, speed for passive damage and armor to sustain.
Speed and sustain. That's my key to victory. With ultra speed you are almost sure to hit when ganking with 'e'. Then you have enough sustain to spam abilities.
Get one of each early to be versatile. Then max w to get sustain while you build up speed items. Then max ''e'' to be effective at ganking. Finish with 'q' to kill all the things!
Smite to jungle, ghost to gank and buff the passive.
You will not be the big deal until you get trinity. Then you should start to be a pain in the ***. So try to take your time farming. Early ganks will be used to make enemies fall back and use their flashes.