There are a few different schools of thought when it comes to the best flooring for a playroom. Durability is certainly important, but so is comfort. If you're interested in a hard surface floor, opt for something that won't scratch or dent too easily, such as laminate, and something that has some cushioning such as cork. Consider laying an area rug over it in order to provide some warmth and comfort. If carpet is more to your liking, be aware that it likely will get dirty. Have it treated in order to make cleaning stains easier.
While a chalk wall is certainly not a must, it's a fun way to give your kids a place to create. They can draw on a whim and erase it just as easily. It's also a great place to draw large-scale pictures. If traditional black or green chalkboard paint isn't to your liking you can always make a custom color by mixing paint with unsanded grout. Just make sure the kids know it's the only wall that it's ok to draw on!
*A note about safety—in children's rooms it's very important to make sure that any furniture above waist height (ie bookshelves and storage units) is properly secured to the wall. Kids have a tendency to climb when trying to reach things and unsecured furniture can pose a serious risk.