Thanks for the comments. Even these few posts have given me the inspiration to finish this first demo. Hopefully I'll have it done in the next couple of weeks. All the ideas are there, but I need to do the graphics and sound, and they are slowing me down a bit. I'm not an artist by any stretch, so it takes ages to get graphics that look just about OK.
@Havie - I didn't think of posting any tips on the Blitz thread, but, as you've mentioned it, I'll start a thread with explanations of how I did various things. None of it is mind-blowing, but there are some tricks that I have used to try and squeeze some more speed out of Blitz. Hopefully it will inspire some more Amiga Homebrew