I would like to know the project steps involved in constructing a gas
station (service station) and car wash. The station is going to be
built in Chicagoland region. The gas station will have around 3000 to
5000 sq. ft. convenient/food store.

Please mention the project steps involved, the permits required, the
project costing, timeline, contractors/professional that can be hired
for this task etc.

These people are experts:

http://www.monitorinc.com/contact.html

Can't help you with the gas station part, but I know of a firm that
call themselves the car wash experts and they build and install
self-serve, inbay automatics, conveyorized, truck wash, and building
vehicle wash systems. They are called Advanced Cleaning Technologies.

Their url is http://www.actcarwash.com/