Publishing: Lulu

I still want to create an actual book for my project as I think it would be the most appropriate format considering the subject matter. Now that I have got a lot of research done and a few interviews back I'm gonna start putting it together and designing some spreads.

The site we were told about was lulu.com. I need to know what size to work to so here are the sizes they produce:

These are the sizes for a paperback book. I have decided to do a paperback even though they do offer the option of hardback. This is because no magazine or newspaper has a hardcover. I want the publication to be in a similar format to a magazine. The standard magazine size is 8.5 x 11" trimmed and folded which is the same as US Letter, a bit shorter and fatter than A4. I'm not quite sure which size to go for, theres almost too much choice! I think I might start off using US Letter and once I've got the content in for a couple of pages, I'll see which looks best. This is their formatting tips for this size:

 These are the binding options they offer for paperback:

I want to use perfect binding because I think it looks a lot more professional and it allows the pages to be spread out easily. Most magazines either use perfect binding or saddle stitching but I think I want to go with perfect binding.