If just starting out stick with Serial, 115,200 baud rate is possible especially if you use handshake, and so much easier to add a pc comm port to monitor the traffic for debugging
Also when you do use comms between micros think about using simple command bytes no need for a full string like "Move:left" can be simply enumerated as follows
use a value to mean a function or direction etc.
0 = stop
1 = right
2 = up
3 = down
4 = left
5 = go
6 = step
in your code use something like this so its nice for you to read
(cut and paste from a web example as i felt lazy lol)
enum MyEnumType { ALPHA, BETA, GAMMA };
Then the following lines are legal:
int i = BETA; // give i a value of 1
int j = 3 + GAMMA; // give j a value of 5
machines are simple, keep it simple makes life easier and quicker 