You can do a search for timeriffic in the Market. It basically lets you schedule how you want your phone set. For example at 7am it automatically turns wifi off, ringer and notification volume down for work. Then at 4pm when I get home it turns wifi on and my volume back up. At night it turns my notification volume down to 0 so I don't get woken up by those pesky emails from work
. As far as the wifi vs 3g its just a matter of preferrence. I like having my data going through my own network when I'm home so thats what I use. If its too much of a hasle then don't bother with it. How much 3g drains the battery is really based on how good of a reception you have. If your near a tower then the difference between the two will probably be minimal IMO.