Default [Q] Increase /data section

Hi, as anyone knows the moto g hasn't a slot for micro sd card.
I have a 16 gb version of G and it's about 12,92 gb available. Let's say it's 13 gb.
I cleaned some apps** from /system/app and system/priv-app.
**useless apps for me (Motocare etc), old apps that has a new .apk in /data (youtube, fmplayer etc).
And now I got 411 mb of free space in /system section. (And I think I can increase a little free space in /system if I'll deodex apps)
And I got 639 mb of free space in /cache section.

My question is can we take this free space and give it into /data? What for we need so huge /cache section?
For example can I keep ~20 mb in /system and ~50 mb in /cache and take the rest 980 mb and give it to /data? And it'll be about 14 gb of available storage.
I never did that. I know that it's not easy to do and while I'll be doing this I can lose all data. But anyway I will appreciated to everybody who will help me with this. May be you did the same on a previous phone, may be there is some guide or somebody already have done this on moto G.
EDIT: and what is /dev section and why it's so big and not using ?
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