My wife just bought me a D100 for Christmas . . . love it! But now I've got the lense bug. I currently have the Nikon 24-120D (I know, . . . but she bought it and it wouldn't be politically correct to take it back). I'm looking to do some nature photography and landscapes, so I need a longer telephoto or zoom lense. I've been looking at various makers and models (80-400 VR, 50-500 HSM, 200-400, 135-500, etc.) and have pretty much decided on the Nikon 80-400 ED VR. The problem is that I will need to save up for it and was wondering if some of the older manual focus (AIS?) lenses would be a good substitute. Some of them can be had for under $300. And given that I heard that AF doesn't work all that well at long focal lengths, or is SLOW, I'm thinking this might be a good choice for now.
What are the issues with using manual focus lenses with the D100? Will I miss many wildlife shots because of trying to focus? Are there any older lenses you would recommend over any others (e.g., 300 f/4)? Should I just get a 1.4x for now?
Any help you can provide in selecting my next lense would be greatly appreciated! Thanks in advance for your time.