Hi,
Nice to hear you are enjoying playmaker
Have you looked around in the
User Tutorial Wiki page?
Maybe some tutorials can get you familiar.
For the layout for the shop you can look to unity tutorials (search for 'unity ui shop')
For the mechanics you might want to get a 3rd party asset like (for example Stan's Assets) if you need real money purchases.
I will see if i can make a tutorial soon for a basic shop system.
I have not really played subway surf so i do not really know which way it is implemented.
So if you can give more info about how it is implemented there
For the colliders, yes you can set multiple collider actions with different tags.
But i think best is to make a object on the top side (child) from the obstacle and use that collider so you know the player collides on top and is not hit by the collider (frontal)