1. Most of the info I've seen suggests every 30 shaves or so. (I believe the wiki says every 30-300, but since every other mention I've seen was closer to the 30, I'd say it's leaning that way). Of course it also depends on all the stuff Gugi listed off.

2. Is the razor damaged? Or is it a razor that someone just shaved a few too many times with without refreshing, but is otherwise in fine working condition? The first case, yes it could take several weeks. The second, I'd argue you can pick up a razor and manage successfully the first attempt. Unless you're a butterfingers, if you buy a shave-ready razor, all you're going to need is the second skill (the really easy one). As gugi said, if you want to start repairing eBay razors, it may take a bit more time.

3. +1 to Gugi with the addendum that razors from eBay take UP TO a few hours. I've had some that got up to shave ready in a matter of minutes. On the other hand, my most recent one is a Big ol screwed up wedge that I've put maybe 12 hrs in already, and it's still not where I want it. Some razors that look fine will wind up being a LOT of work to fix. Some that look trashed will take a couple minutes rubbing off rust and then a few strokes on one or two different hones and you can shave. It's a gamble.

4. Touch up hone? Three cheap options are: Swaty or similar barber (eBay, $20-40). 6k IceBear King (~$30 WoodCraft). 12k Chinese polishing ($20 WoodCraft).

Swaty's are fine finishers, 4k IceBear is acceptable as well and I'd expect 6k would fill the "finisher" role a little better, I don't have experience with the 12k China Stone, but it's pretty popular as an entry level finishing stone. There are other options available, but these are probably the three safest and cheapest ones.