Unfortunately you cannot use AA batteries with the E-510. And it takes 4 HOURS to charge the battery. I have ordered another battery from UK for very little. On a flipside the battery does last a long time even with liveview but longer without.
You can get a extra grip from Olympus (Link at bottom) along with all the other extras you need.
As for the IS, it comes in two types IS 1 will stop all movement, i.e vertical and horizontal shake. IS 2 will allow horizontal shake for if you want to pan the camera like following a race car etc. and allow for blurring with creative shots etc.
I am not sure how many stops it allows but it really does help a great deal.
http://www.olympus.co.uk/consumer/dslr_ ... _Chart.htm