I have used Rapidash as a part of a synergetic core, but also as a offensive mon on its own. It's strong, fast, but lacks defensive strength. I don't like using it because it's pretty weak to stealth rocks and entry hazards, and it doesn't like switching in when it's not a safe switch. You end up saccing one of your pokemons or you have to switch in against a fire user.
I would use support with Rapidash, like seismitoad or mantine to back it up, but it's quite a pain to get covered though. And once it gets going, it can still be stopped pretty quickly, although it outspeeds. I'm not too fond of it as a sweeper or offensive mon, but as a part of a synergetic combo, it can work.
Life orb is good on RDash, although it will take it down fairly quick, so I would go with heat rock or leftovers instead, but that's just my opinion, as I find it too easy to kill if you put life orb on it. It will take so much residual damage that it'll fade away too quick for what it's worth, so yeah, I recommend the alternatives above life orb.
<+chieliee> .tell chielieee HELLO MYSELF
<skybot> chieliee: I'll pass that along.
* chieliee is now known as chielieee
<+chielieee> sup brah