the front mech kind of does the job of most xc type chain retainers, you will notice what a good job it does if you try to ride anything rocky without using a retainer. if you want something more robust look at an e13 lg1+ or similar, with this you can also still run a 32t front ring and you dont need iscg tabs as it comes with an adaptor.
the rear mech, cassette and chain will all be fine, make sure you use a front ring that is the correct diameter for your chain though, dont buy a bmx one or anything.
the crank thing is down to personal choice really, either is fine. some brands such as raceface sell the crnks without rings which will save you a bit of cash but you can always flog new chainrings on the classifieds.
good luck!