On the rail lengths problem I know you can butt individual profile rails together to make longer rails but not seen it done on supported rails. I wonder if you cut off a piece of the supporting extrusion you get with supported rails (say 200mm) and use it to bolt 2 shorter rails together ie a joining piece. Because the support is continuous and has a shallow radius on the top which the round rails sits in it should help align the rails to each other. You could then order 2x 1m rails . Not tried it but something to think about.