1) I have seen the picture - your PCB is basically only around CPU + 1x DDR3. The main question is, what you are going to do with that PCB? Usually, you also need some connectors and these are going to take some space. Will be there some connectors on your PCB?
Possibly, for inspiration, have a look at our TinyRex - that is one of the smallest things we ever designed. It may give you an idea about what else you may need on your small PCB: http://www.imx6rex.com/imx6-tiny-rex/
2) We also sometimes route ADDR/CMD/CTRL signals on different layers. Just be sure you are careful about what you are doing - for example, you may need to consider the length in VIAs and also length routed on the TOP/BOTTOM layer vs Inner layers.