Need some advise for changing from brushed to brushless

[stebedford]

Ok, so I know about the different types of brushed motors and esc's out there at the moment but when it comes to brushless I havent got a clue, at the moment im running a 15*3 brushed motor, I do want to change it to brushless, but no idea what the different types are, whats the difference between the number and stuff? what speed controller and lipo would I need for brushless motor, ive seen people talk about 8.5 motors but still no idea what the difference is between an 8.5 and 13.5

If anyone could shed any light on it I would be greatful, and also any suggestions for any cheapish/beginner brushless setups would be great