Can someone help me how the fuel level in a vehicle tank be measured?
What sensor can be used?
What other features can be added in order to automate a vehicle?
Is the electronic lock system be added & how to give information to user mobile when a burglar tries to open it?

The fuel level is measured with a fuel sensor - use only approved fuel sensors otherwise you risk explosion. There are all sorts of vehicle automations e.g. cruise control, but almost all are rarely done since the effort in installation and custom mechanical work is prohibitive. If you have lots of time and money you might look at hot rod sites which discuss all sorts of mods. Regarding the car alarm, using a celluar modem connected to a commercial car alarm sounds the most straight forward.