Is this doable in WordPress? Client wants WordPress

Hello, i normally make my websites from scratch with a CSS template and costum PHP / JS, but a client WANTS me to use WordPress, so i want to know if i can do this in wordpress:

Make a site where every new user has has his own blog, make a few themes for those costum blogs, and hardcore some PHP in to the blogs, if yes, could you point me towards relevant resources and plugins?