Creating a car chassis takes about a week to complete. The car’s body takes like one to two weeks depending on how detailed the car would look. Since your game will rely on its game engine, this takes months and even years to perfect, you would obviously be adding constant updates and roblox updates might break some things, so yeah.
I haven’t hired anyone yet, so I wouldn’t know how experienced a person should be to create these things. Probably 2-3 years of experience would be fine since a game’s framework is complex stuff.
It would depend on how active your team works on the game. Even with a full team of developers, it would take at least 5 months to a year or possibly longer.
It is very hard to predict how long a game would take to make as you have to consider multiple things. It would depend on how big your development team is as having two people is certainly quicker than having one person. You will need to consider how experienced your team is, as in theory the more experienced you are the quicker you will be able to do something. As the OP said it would depend on how much time you put into the game each day.