First up, I'm going to shift this over to "publishing", which deals with these sorts of topics.
On your first question, you may find some things in this thread
on Gimp (shareware equivalent of Photoshop), resizing programs, and image hosting and linking in the forum. If you get a free Flickr account, for instance, the site automatically creates images at a few different sizes from what you upload. So that might be your best bet and kill two birds (resizing and posting images) with one stone.
On the second, this thread
and this one
have some thoughts.
As to the third, I think the key is to break up straight lines. If you are building up the ground with green plates, for instance, I always try to make sure that there aren't just long unbroken straight edges. For instance, in this picture
, you can see that I tried to make very irregular patterns in the ground. This becomes even more crucial when building up a hill, as long flat stretches look like a wall. Or if you are using BURPs, I try to disguise them so you don't get that repeating pattern. Here is an early MOC by me
that was very unsuccessful in doing this. This
was, IMO, more successful. More recently I've gone to doing cliffy areas all in one color. While I think a mixing of different grays is more realistic, it becomes kind of "busy" to photograph against.