I'd recommend the 4k/8k combo. Assuming the razor's edge is in good shape now, you might be able to get it sharp with just the 8k, but eventually it's going to need something a bit more agressive. Additionally, if the razor is NIB, you'll probably need to develop a better bevel on it anyway. Get the combo, you increase your options. Another might be to get the single grit 8k now, and a single grit 4k later. The thing is, the combo 4k/8k won't cost any more (and probably less) than the single grit 8k. All it takes is a stray piece of dirt or grit, and you're gonna want the 4k...it'll take a week to work even a small nick out with the 8k. The number of strokes depends on the razor. I'd recommend getting a less valuable one to practice on until you develop the feel you'll need to get it right. The pasted strop will go a long way to keeping your edge up before it needs real honing again. So, unequivocally, get the 4k/8k combo stone. Just my $.02

Joe