[MOD] Use Android without Lockscreen

hi to all!
I would like to modify Android in this way :

1) When i'm in the desktop , must be start a count Y and at the finish of Y there must start lockscreen in automatic.
For example( Y=15) after 15 second that i'm on desktop and i don't touch monitor must be start lockscreen

2) when i'm in any application or menu must be start another counter (X ) (when i don't touch monitor) and when X=0 dysplay must be off.
For use dyplay i want to touch monitor and display must go ON .

If possibile i can use:
-SDK developer
or
-MOD rom
or
-tasker.

Is this possibile? use more more battery if i poweroff only monitor?
Where i can do this?

thx!