First nice to dive into WC, I did it and love it
second check this thread out http://www.overclock.net/t/226970/updated-water-cooling-essential-threads
check all those threads and it will answer a lot of your questions.
last to actually answer your 2 questions a. two pumps in serial does increase flow, but you will probably not need it if you get a solid pump. b. i would do whatever gives you the cleanest looking loop, easiest to drain/fill, and lastly uses the least amount of tubing.
this is generally something like Res>Pump>CPU>Top Rad>GPU>GPU>Bottom Rad>Res
this all depends on where your res and pump are, but it is best to have res right before pump