AFAIK there is no requirement on the number of downvotes for autoreaping. Autoreaping will happen when a consideration-vote is cast, if the reputation is negative (can be -1 with a single vote) and there are at least 5 consideration-votes, most of which are "Reap" (the condition is more complex than that, the number of Reap votes required depends on the number of Keep votes). Someone mentionned -$NORM, which might be a better idea (yes, a -10 reputation is hard to reach, but I like the overall culture of forgiveness of perlmonks and its reputation system).
Discipulus is the one I've seen mention the reduced font solution the most, maybe the one who proposed it in the first place. But unless you can force the font size on some content, the user could just redefine the font size to ignore the one applied globally to the node. Adding a warning at the top of the message might work. I also like reap-like replacement message where the node is replaced by a message stating that it is below some threshold reputation. It could be the default when viewed as Anonymonk, are require activation for other users.