Without a pull start, you bump start it. Get the bike rolling, drop the clutch, and the rear wheel will turn the sprocket, clutch, crankshaft, piston.
Shifter: without a shift kit, the engine drive chain is on the left, and the pedal chain is on the right. Never the twain shall meet. People will often move the pedal gear shifter to the left side of the handlebars, because it doesn't mate with the throttle assembly nicely. If you install a shift kit, this includes a jackshaft and pedal crank sprockets which causes a short engine chain to drive the pedal chain: the only chain to the real wheel is the pedal chain. Therefore, the engine will go through gear shifts just like the pedals would. Without a shift kit, it's single speed.
As far as the HT 2-stroke kits are concerned, they're all essentially the same as far as performance and manufacturing quality is concerned, and that can be a little dodgy. Buy from a vendor who will offer a decent warranty. eBay can be drastically cheaper, but don't expect any after-sale support.
Kit parts that people often replace: plug wire and cap, spark plug, engine hardware. But it's not necessary to replace these things immediately. If installed with care, and if the kit parts are not defective out of the box, the bike will run just fine with the stock parts.
Some kits come with a u-bolt style front engine mount clamp, some don't. Don't drill through the frame under any circumstances. If you need, you can fabricate your own front mount from hardware store bits, or there are vendors that sell them. (SickBikeParts sells front mount brackets in a wide variety of sizes.)
The wiring from the CDI to the mag should be soldered and heat shrink tubed; the quick connectors that come stock are unreliable.
Overall, be patient, take your time. Make sure your rear wheel sprocket is installed straight and true, make sure the engine is mounted evenly and solidly to the frame, and make sure you have proper chain clearances and tension. Everything else is peanuts compared to those things.