They're three entirely separate things.
EGR is an emission control device targeted specifically at reducing combustion temperatures thus lowering the production of NOx during the combustion process. Unfortunately it also results in increased fuel consumption and increased soot in the exhaust stream.
The catch can attempts to remove oil from the intake. As combustion occurs inside the cylinder, some of the gas escapes past the piston rings entering the crankcase. To prevent this from pressurising the crankcase and causing other issues, there's an opening in the top of the camshaft cover at the rear that allows the gas to escape. However, because it's super-hot, it also carries small quantities of vapourised crankcase oil. All of this is reintroduced into the intake manifold so that the oil vapour is combusted rather than being sprayed onto the road. Catch cans are NOT vital and you don't really gain a lot of performance by using one. You DO keep the intake cleaner and this is more important if you're using an intercooler.
A Dawes Valve controls boost. Depending on your turbocharger, you may or may not need one - see bods' post, you probably won't.
