99.9% of the time, you should glass it all at once. You will find that a subsequent layer wets out in 1/5 the time as the very first layer, mostly with excess resin from the earlier layer(s). As you bubble roll it with your finned roller, you will find the dry spots that need more resin. The first layer is the slowest to wet; subsequent layers should really fly. On a large part, like a kayak, use a slower mix and/or cool the room and maybe cool the mixing cup, too. If you are new to building with FRP, you should do some smaller practice pieces to build up your skills. I like to buy from http://www.jamestowndistributors.com . They have a great 5.8oz carbon fiber 2X2 twill which conforms very well, and many specialty fabrics, in addition to standard E-glass.