My first suggestion is that you should really go from the basement waterline. It is worth doing more work to get water from your mainline so you can have more pressure, therfore, having more sprinklers on a zone. If you still wish to come from the washer line, use 1/2 copper from the pipe to the washer, to the backflow device, then come out of the device with 3/4" PVC to your valve manifold.
Then, use the 1" Flex pipe (I am assuming poly pipe) from the valve to your sprinklers. It is ok to use the 1" pipe that you bought.
It is also worth using the valve manifolds that you can order. They are alot stronger than manifolds that you make. My suggestion is to use the ordered manifolds.
Hope this helps!!!