I tried to post 5 photos all around 150kb but when I preview the post only 2 show up and the others just have an x with numbers. Is that normal?
Yes, that is normal. Go ahead and post and the rest of the pics will show up properly in the final posting.
I always adjust mine up to 194 KB or as close to it as I can get, but limit the height to no more than 720 pixels, even if that makes it under 194 KB, so it will fit the screen without scrolling.
194 KB doesn't show up a lot bigger than 150 KB, but it's a little better.