Well if the cars are on your property I assume they are not strangers, and realistically a Syma won't do much damage hahaha. I had a 3 pounder have me loose 90% control, it went down 10 feet from a bunch of cars on a farm where our we were having a camp for some kids with my church. No...
Well most low KV motors are havy and something like a 12S battery would mean you might as well strap a brick to the quad. That is why I said theoretically, it is practical for a 500 class to go HV system, but the equipment is too heavy for a 350/250/180 (unless designed to do so).
Yeah, lower KV motors and bigger props generally increase the thrust, but at the sacrifice of agility, speed and some stability, but if you have higher voltage you can use lower KV motors for smaller props and it is theoretically more efficient.
With those legs you might need something to protect the board on top if you flip, and maybe something breakaway as if you have any forward momentum they would be prone to break.
first you are going to want to get a cheap flight controller like a KK2.1.5 to check all of your hardware with.
Take a look at this post, some of the info pertains to this.
A little due to the resistance, but should not make too bad a difference unless you are doing a LRS, if you want you can solder a new connector on your Rx or Tx.