To get rid of the rough edges turn off pixel rounding and set sampling to linear in project properties..
You are going to have to make a choice though..
A beautiful pixel-perfect game or a game that is actually playable..
Nobody is going to notice a bit of stretching of sprites in the background and it could save a lot of memory..
Turning of collision does help a great deal..
Using the tilemap works too, although you should decide later if the effect is nice-looking enough, else you could always create the sprites again at the tilemap positions.. (Creating the layout using tilemap is much quicker)
Be sure to use tiledbackground and/or 9patch as much as possible, for it reduces image memory a lot too..
If the game runs smoothly on a desktop, it will run smoothly on WiiU, so that's a good indicator..
turning off collisions of unused object (sprite) DONT HELP or Change anythings
because collisions are checked if you use collisions action in even sheet ....
however , i would like to understand about creating layout using tilemap ????