There should be a market for devices that sit between your wi-fi modem and the ethernet cable that fulfill these firewalling needs. For security + convenience,

There should be a market for devices that sit between your wi-fi modem and the ethernet cable that fulfill these firewalling needs. For security + convenience, they could be set up so that the internet can't update or configure it -- rather, you have to insert SD cards to upgrade or change rules. (Maybe the device already comes with "Full paranoia", "Dissident blogger", "All-family", etc. cards in different colors; updates are downloaded from the internet otherwise).