1. Repeaters on the Cyan line should be set to 3 ticks. 2. Repeaters on the Blue line should be set to 2 ticks. 3. The wood used in the tree farm does not have to be OAK would, but it has to be a form of wood (No planks) 4. The pistons only have to be 6 blocks high (this will save on resources but involve a lot of redesigning on your part)
If you are having problems with this build I would highly suggest downloading the world and taking a look at what is going on.