A series of Vehicle-related queries. Can anyone help me here?

There's a few things I need to ask here, so I'll number them. here's where I'm at: we're designing a car dealership for a game we're building and we're fine. The only issue we have is we don't know how to set each car's owner to prevent vehicle theft, how to set the game to remember across servers which of the cars each player owns, how to set up a buying system, and how to spawn/delete the cars. so, my questions are:

1) How can I set up a system to detect a player's money value (a statistic that will be held as a leaderstat) and purchase a selected vehicle by clicking (need clickdetector) a specific brick?

2) How can I set the game to remember which of the cars each player has bought? This is so that players do not have to buy a car again every time they join a game

3) How can I identify a spawned car's "owner", meaning the only player that can use the driver's seat?

4) How can I create a system (possibly using a GUI) that will allow a player to spawn any of the cars they own?

5) How can I set up a system to delete spawned individual cars?

I know that's a lot to ask for, but none of us can figure it out for the life of us - even by going through this and similar websites to find answers. Either what they were given doesn't work anymore or never worked at all.