The 8 inch coil would be a great addition to your 'arsenal' it will get along better in trash areas than with the 10 inch coil, the 5 inch EXcelerator would be a nice option too, they go deep and are extremely useful for very high trash areas.
Sunray makes great accessories for the Explorer S, XS & II, including the invaluable X-1 Target probe http://www.sunraydetector.com/sun_ray_x-1_page.htm
which is like having a 1" coil attached to your detector, it runs on your detectors batteries, it's lightweight and mounts on your unit, etc. Click the link I gave you, the info should be there.
Sunray also makes great coils, I don't own one but they certainly have a high reputation for being equal if not better than the Minelab coils.
http://www.discountdetectors.com/ is the place to buy your Explorer II if you want the X-1 probe included with your Explorer II instead of just sending your detector lower/upper (don't remember which) rod and wait until they install it and send it back, and you'll get it at a discount price, so you really can't go wrong, that's where I ordered from, I got free shipping and accessories. And the guy who runs the dealership, Ron Dugger is a great guy to deal with!
Another type of coil to consider is the 15" WOT (Wonderful Orange Thing) from Coiltek http://www.kamakazi.com
Many people here tell it's a great coil, with great depth and sensitivity for small items like dimes, etc.
The things that you should concentrate on getting (In my opinion) with the Explorer II are the following:
*Sunrays X-1 Probe.
*Sunray's Stealth X-8 coil, or Minelab 8-Inch coil, or the 5" EXcelerator coil from Kellyco.
*Predator Tools Model 85B or Model 31 "the Raptor" model (each have a 5 year warranty) http://www.predatortools.com If you're looking for great relic hunting tools, this is the place to get them. Tools made by Predator Tools are by far the best, and won't let you down, nor they will break.
*Jimmy Sierras "Treasure Scoop", for me it's an invaluable piece of equipment, it's made of ABS so it's increadibly tough to scratch coins with it, you can scoop a large amount of soil/sand with it and you can scoop dirt and pass it on your detectors coil to see if the target is in the scoop. http://www.jimmysierra.com/
*And a Sand Scoop (metal prefferably) IF you live close or nearby a river, lake, beach, etc. And you're planning on hunting it.
*The book "Mastering the Minelab Explorer XS & S By Sabish" is optional and a great book in helping you understand your Explorer better.