You got some good ideas above and I will add a few things to look for that might help you.
A 2 gig flash card will hold average of like 500 normal photos at 6 megapixel.
but if something happen to your card you are to loose more that way I would get several 1 gig cards.
you can get these around 20 bucks and less each.
the battery packs on slrs work and last long these days,
1 you could get a 12v charger for the cameras battery pack or
2 get a external battery pack grip for the camera you pick and use AA batteries and you could also
use these for your flash. you could also use rechargeable AA batteries with a 12volt or wall charger but I have no idea
what they have for power sources there.
This would be a good time to pick your future lenses you may like also.
the nikon d40 and d40x has to have lenses with internal focus motor so a lot of nokon lenses won't work on them body's
most all will work on the d80.
for what you list I think the d40or d40x would be great for you and the 18-200 would work fine also ,i don't think you can
get the external battery pack for these cameras . the d80 you can get the pack and use AA batteries.
canon rebel cameras i think you can check and get the external battery pack for.
also i think the pentex do also.
the metz 58af is a great flash and same for nikon sb800.
this is not a great place to skimp and buy the cheapest,you can get by with a cheap lens but not a flash.
if it don't have the power needed your shutter speeds will be slower and even under exposed you have seen these type photos from some body's point and shoot camera I know you have that's what a cheap under powered flash will do!!!!
get a good high power flash, yes it cost more but you will have it for years and you will be thank full you went that way.
will the pop up flash on these cameras work ,yes ,BUT WAY UNDER POWERED.
I am sure after you get your camera of choice you will take photos of the kids or grand children etc ,trust me get a good flash.
you can stick to the 6-10 mega pixel range and have a great camera set up.
I have made lots of great 16x20 school sports photo's on a 6 mega pix camera in the past.
i dont know how to list these but i will try maybe it will work,
www.bhphotovideo.comhas tons of photo gear and i have used them for years,very well trusted company beware of a lot of others.
the gallon bag is also a great tip you got carry one extra with a hole in it and put around your lens shade with a rubber band and shoot in the rain if needed.
i would get a uv filter to protect your lens from dirt on the class,you can clean this and if it gets scratched get another one and alot cheaper than a lens fix.
a cheap 30-40 dollar tripod from like walmart may come in handy,also a camera remote or a corded shutter release.