SRAM vs Shimano seems a lot like the Microsoft vs Apple debate to me really!
i.e, both products are good, but it comes down to personal preference. Note that the mechs (at the higher end) aren’t cross compatible. So if you already have the SRAM shifter you’ll want to get an SRAM mech, maybe X7 or X9.
No idea on the BB and crankset to be honest mate. Check out bike radar reviews?