Phone I am lost help please

Here is my story me and my galaxy not 2 :
i had android 4.2 so i decided to update it to kitkat 4.4 and i installed it wit omni .
after finished i found the camera not working . i did alot of search to fix it but no way .
i tried to downgrade it using SDK but i couldnt put the device into fastboot mode .so i used odin to instal slim 4.3.1
my problems :
1- my internal storage is 10 g i am using about 2 g with the slime 4.3.1 but when i checke storage it says just available 2.5 g
and when i am in recovery mode i can find the old files .
2- WI Fi so slow

so any one can help me with that sad story??