Will it make battery life better, phone faster etc if all I do is root?
No. Most people who root do so to remove bloatware and/or install a custom ROM. Rooting, and doing nothing past that, only gives you superuser access to the system, there are no other advantages that I know of beyond that.
You can get better battery life by calibrating your battery. I have done this on several Android devices and it has been beneficial.
Calibrating the battery - my take:
1. Run the phone until it dies due to lack of power, it won't take long on a new phone
2. With the phone off, charge the phone for one hour past the point that is appears to be full
3. Reboot and repeat steps 1 and 2 a few times
4. You should only have to go through this process once in a while, such as flashing a ROM
After the 4th or 5th repeat of this process, you'll begin to notice that the phone is more difficult to intentionally run to the point of dying due to lack of power. This lets you know that the process is working.
I have been doing this on multiple Android devices and I'm now getting around 20 hours on a single charge, with moderate use, out of my Evo 4G. I was getting around 35 hours out of my Samsung Vibrant and 20 or so hours out of my Motorola Cliq XT.
A note about bump charging: Don't do it, it lessens the overall battery life.
Bump charging is the practice of charging the battery to full, unplugging the USB cord and immediately plugging it back in. This will give you a boost in battery life but it is bad for the battery in the long run.