I’ll keep sharing more notes about past and future development of Crabby Ball on this thread:
Translucent sprites
The first issue you will face when working with sprites with translucent material from using .PNG images is the drawing order problem. I assumed first that setting different depth (Y coordinates) will be enough to create the layers of my game… FAIL! Translucent materials in 3D engines are sorted by object position and they not take benefits of rendering Z-Buffer. Then the magic property is: “Translucency Sort Priority”, from Rendering category of sprite details.
Here is the problem and solution on answerhub (Thanks to Eric Ketchum for the help): https://answers.unrealengine.com/questions/146920/z-buffer-problems-with-paper2d-sprites-using-trans.html
**Unstable Physics **
Would be very bad if your gameplay depends on Physics and it behave different when running on different devices with changing frame-rate. Using console command t.maxFPS 40, I though was good to limit frame-rate to safe some CPU usage but while the game runs always fine in my PC when playing it on Galaxy S2 sometimes the ball behaved like having half of its gravity force. Removing the console command fix it, but my game is still not completely safe of glitches, specially when the level have just loaded the player jump and send the ball at very high speed… I managed to clamp its velocity vector after any impact but this is not very nice solution.
I have tried sub-stepping and many configuration combinations until my game is acceptable but I’m not completely satisfied. What I’m think is to avoiding, making my game-play depending on UE4 physics next time 
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** Android compatibility and package size **
A lot is already said about this subject here in the forums and answerhub. If you are making a simple 2D game you will enjoy the developing process but your game will suffer a big disadvantage on google play competition because your app will require a nice GPU and more than 36MB (minimun download), while a similar 2D game made elsewhere will run on almost every phone with less than 10MB of download size.