You can have any site on any plan.. we just grouped them that way because in most cases the business sites will need more space and bandwidth, and most businesses tend to upgrade to the business account. So it shouldn't be a problem

The addon domains are unlimited. We just keep it on a set limit for control and server resource purposes. If you come close to the pre-set limit, just let us know and we'll extend the limit. As for bandwidth, we can charge overage at $1 per GB if requested, but in most cases it's much cheaper just to upgrade to the business account