As with most forums, you need a seperate hosting site. There are a number, i use Flickr, but just stay away from Photobucket.
As for how your post your images, thats up to you.If you want to post some of what you have already built, then you could post them all in one thread. But for an in progress build, most do a thread for each one.
I am a Norfolk man and i glory in being so
On the bench: Airfix 1/72nd Harrier GR.3/Fujimi 1/72nd Ju 87D-3