Forum Moderators: open
To answer the question - there should be no problem with cross topic linking within a site.
My viewpoint is that these sorts of sites already exist for my clients but are owned by third parties (affiliates). What I have done isn't any different to what others have done independently, I've just helped nature take it's course, so to speak.
Googles spam filters are fairly simple and don't pick this sort of thing up so you are fairly safe for the time being. I would just make extra sure that you are not breaking any of their rules. They don't explicitly say that you cannot own other domains that point at your own domain so in that sense you are fine.
good luck
eplus