When I first started taking photos of my Hannover build, I was using a small Nikon that took 10 Mega pixel photos. The problem is that it has no real way to focus it or adjust settings to get a better depth of field. When you focus a camera there is a plane where things are in focus and items closer and further away will be fuzzy. The best depth of field comes with a pin hole camera believe it or not.
When you do extremely close up photos the depth of field is usually quite thin. The only way to get it where more is in focus is to use a camera with an adjustable aperture that can be closed way down. This gives a bit of a pin hole effect and allows more to be in focus. It also requires a LOT of light!
I ended up going back to my fancy old Olympus 5 mega pixel SLR camera. I can set the focus where I want it and see that it is in focus. I also usually adjust the aperture as small as possible, use manual focus, and the built in flash with a piece of mylar in front to diffuse the light a little. This gives a lot of depth to the photo especially in Macro mode. The little point a click cameras with everything automatic just don't work as well for that kind of stuff. The 5 mega pixel Olympus weighs in at about 3.5 pounds with the battery pack and all, but it works so much easier and better than the Nikon. I can also add some additional macro lenses and get it to go even closer.
As to the resolution, 5 m is plenty for what I am doing in the posts on here. A 5 mega pixel photo can do a very sharp crisp 8 x 10 photo at the photo lab. Much more than what is needed in internet posts. Best way is experiment with your camera. Get a photo viewing program and experiment. After all it isn't like you have to go and develop film and get prints to see what worked like in the old days.
One other thing, is a decent photo editing program. Adobe has Photoshop, and there are a number of other programs out there. Sometimes a photo is "almost" there and it just needs a little tweak in some way to make it much better.
Here is an example: A painted miniature with small parts from my Hannover build on a black background. The dime gives you some idea of the actual size of everything. Original size of the photo was 2560 x 1920 pixels. After cropping and resizing for posting, it is 800 x 692 pixels. Both photos look pretty much the same on the computer though the large one is 2.7 meg and the small one is 75k. The sizing was done on my photo editor of choice Corel Picture Publisher.