Okay one problem at a time....
First >> Brightness
I added the two patches( gfx>>igpu; brightness hd3000/4000 ) and use the patched acpi-backlight.kext
But still the problem persists, of being able to change brightness only once per login, then it becomes unusable.
What do you mean once per login?
So... if you go to SysPrefs->Displays and change brightness, then logout, and go back to SysPrefs->Displays to change it again it doesn't work the second time?
Also what is the diff b/w, and which should I use??
First is to avoid instant wake (and other problems caused by USB). Second is to multiplex USB2 (EHC) with USB3 (XHC) for use with AppleUSBXHCI.kext (not necessary if you're using GenericUSBXHCI). There are comments in some of the patches. You should read them.
my battery indicator works with just the acpibatterymanager.kext should I also use this patch, it says 3251(which is my laptop)??
I only see "Dell 3521" in that patch (not "Dell 3251"), but as for your question..
If you have working battery status without DSDT patches it could be because of two reasons:
1) You installed Snow Leopard version of AppleACPIPlatform.kext (will break proper power management and possibly other things, such as sleep)
2) Your DSDT does not require patches (if there are no EC fields larger than 8-bit that are accessed directly or indirectly by ACPI battery methods)