Don't know what you mean by "normal", it's whatever design the manufacturer uses for their laptop. There is no single standard way to design a system. I have seen quite a few laptops with only one RAM slot. Not a very good design for upgrading but it's "normal" I guess.
About swapping the motherboards, you would have to contact Lenovo or do a lot of research about exactly what the differences in the models are. You may find out that the motherboard fits, but the video connection is wrong for your screen or some other connector is 1 inch further and your cables can't reach it. I would just sell your laptop and get one with the motherboard you want. By the time you are done buying things, testing it, you would have been better off...