Following on from what Torealis said, which I'd pretty much agree with, you don't have to take 20 assault marines. I'm also doing a battle company with support, but I've only taken 10 assault marines - the other assault squad is split between the bikes and speeders. From my reading of the codex, it looks like this is how a company is organised, though of course, others may disagree, and anyway different chapters (and even different companies perhaps) have slightly different organisations...
Hope this helps.
Hope this helps.
