How to handle multiple client with one project ?

obviously you can use single database and application to handle multiple clients.

its like you have two clients say GoldSubscribers and SilverSubscribers

The GoldSubscribers may have access to more functionalities than the SilverSubscribers.

Better is to create a lookup table for your clients with their roles and when they login based on their role you can show them the menu.

you also need to dynamically change the layout (Like menu and client name) for this you can create a table called menu which will contain the navigation links and assign different menu id to different client and then in your layout show menu based on the client Id.

there are lot's of ways , i just suggested you a scenario-solution.