Be prepared! This is a big bite you're taking.Remember, you want to be sure that all seams are watertight when you're finished; wall (presumably tile?) to base and base to floor. But you can do it. Just take your time and don't panic. Make sure your base is level and put a shovel full of concrete underneath the base itself to give it strength(then step onto the base before the concrete sets). Then caulk it nicely.
Re 12x12 tiles on a wall - these MUST go on concrete backerboard with mortar - NOT adhesive. But they will look really sharp. Cutting out for the faucet and taps is tricky, but take it slowly and you will be pleased with the result.