I am going to have a frame re-sprayed.

The bike shop said they can remove the components and put them back after for £40.

I would like to strip the Bike myslef, but concerned about doing it correctly.
I am pretty new to doing the Bike Mechanics myslef and my main concern is the Bottom Bracket, how difficult is it to take this off and put it back properly ? In general is it pretty straight forward to strip a bike back to the frame and put the components back ? or is it worth letting the shop do it ?

On the subject of BB's - the Bike is pretty low end spec right now and I am putting some better components on it - do BB's come in different specs ? and is it worth up-grading this ?

Thanks..