dont worry about being less than knowledgeable on the piece parts to a custom build - - that is partly (in my opinion) what a competent builder should be able to provide you...ideas, what works what doesnt etc
your budget will dictate what you can and cannot get.
Travis at RBros rifles builds some of the (arguably) best hunting rifles you can get. he tests' each and everyone in the field - - like they are intended to be used.
on more of a budget build, Alamo Precision Rifles, will let you customize the rifle to your likings (color, flutings, etc etc) for a very attractive price.
one thing i would emphasis is pick up the phone and talk to your builder, you will hear lots of horror stories on here with no return calls, no emails, 3 year lead times, 1 year missed promise dates etc i would steer clear of anyone that doesnt take 3 minutes to talk to you before taking your hard earned money.
good luck.