No need to apologise! They're perfectly legitimate questions. :)
1) It's not something we've really explored thus far, though it's certainly doable. I've been considering lately ways to go about some broader, game-wide plottage, and that could be one good way of achieving it.
2) The way I've described it in the past is - think of a human life as the flame of a candle, small, weak and limited to the length of the wick. Well, a god's is more like a bonfire, bright and long-burning, its life only really limited by the amount of fuel. Compare a candle to a bonfire - that's a pretty significant difference. And like a bonfire among candles a god has a fairly distinctive presence, one that other immortals can pick up on. In terms of the exact feeling gods get when they encounter this presence, that varies from person to person and there's no wrong way of describing it. Some people have described it as a buzz, or a tickling at the back of the mind, or an itch - really up to the player.
3) We don't really have strict guidelines on journal use. Primarily they're used as journals (as well as for basic OOC info, ie. character profiles), but other forms of RP like answering machines, letters and so on are totally fine. As a general rule, full-on threading really ought to go in the forgotten_gods or forgotten_past comms, but there's no rule strictly against doing otherwise at the moment.
4) Activity would generally count as participation in a thread, whether it was posted by you or someone else. IC journal entries are fine in a pinch, though.