Your gonna love this lol....
Don't worry though, your purchase was fine out of all honesty. It is a good bike. But my experience was crazy.
I spent a month trying to get this thing lined up. I bought the manic mechanic hub adaptor and sprocket for $70 (ever heard of it? It's not necessary, but a great purchase for any bike. It drives the wheel not the spokes). It still didn't help.
Long story short, I took it to a place that builds custom motorcycles, and the total came out to $275 for his mods (O.O OMG SO EXPENSIVE!). I could have bought a new bike! He helped me make a lot of little (unnecessary) mods and other stuff, but what he really did was put spacers on the axle, and took the sprocket, and grinded it down so it would fit closer to the spokes. THEN my bike worked!
Your bike will very likely cost more than the cost of the plain bike and the engine kit. Everyone needs extra parts. Also a helmet, etc. There are members who will just say off the bat that their budget is $1000.
You shouldn't need that much though. What I would recommend is simply putting on your kit and seeing if it works. If you have trouble with alignment, you can buy the Manic Mechanic hub adaptor if the sprocket needs moved out (away from the wheel, the hub can adjust either way though), or a single speed wheel (meaning one gear only, $60) if the sprocket needs moved in, towards the wheel. You would only have one speed (duh), but that's all you need. Then you can use spacers (washers) on the axle to adjust. MUCH cheaper!
Even if you don't spend the money, if you have it set aside, there is a lot of great stuff to buy for your bike!
Expansion chambers will give you extra speed and power, a speedometer is pretty useful, visual mods, and the list goes on.
I can pretty much guarantee the build won't be plug and play for you though. It's a cruiser so you'll at least have to mod the mounts.
It's really a snazzy looking bike though. Good luck!
..Thanks again