Re: first engine kit
I would use one of the vendors listed here myself, the kits come with just about everything you need. Most of the kits are the same, it really comes down to customer service, price and what upgrades they offer. For example some offer a bearing chain tensioner or no drill front motor mounts etc. Or if you're in CA. which ones will ship too you.
That being said, no matter what kit you get there are some things you'll want to upgrade. You can likely get by without it for sometime. But are better off upgrading some things, bolts/nuts, plug and wire etc. Some say the kill switch, I've had my stock kill switch for sometime, but it is something I'll do sooner or later.
Sun Tzu: To secure ourselves against defeat lies in our own hands, but the opportunity of defeating the enemy is provided by the enemy himself.