Ok, I do this for a living, so... first is lighting.
Up to 4x3 feet 2 strobes would have been fine, but any bigger and you'll want at least 4 strobes, and a way to mount each light one over the other... ideally. Anyway you'll want some decent lights with good shot-to-shot stability, like Hensel, Elinchrom or Profoto, don't go any cheaper or you'll want to tear your hair out.
For eliminating residual reflections and ambient light, you'll want polarizing gel filters, Rosco 17x20" are good ones and cost about $40 each, but you'll have to mount them to a frame yourself. Cutting out a rectangle of cardboard and duct-taping the filter to the back is fine. The filter needs to be situated in front of the light like so:
The lights themselves should ideally be at a 45º angle to the surface of the artwork from the sides, so you'd have one light on the left and another on the right for example; it's the most basic setup, but you can't go too wrong with it. With the polarizing filters though you have a lot more freedom in placement, and the light can almost be reflecting in the artwork before it becomes a problem. One important detail is do not use diffusers like softboxes or umbrellas, they tend to defeat the effect of the polarization.
Of course, you need a polarizer on the lens of your camera too for this to work, it can be any kind linear or circular. And do keep in mind that you lose over 2 stops of light using this method, so you're going to need at least 1000w lamps, for me personally 500 is fine.
Next up is... shading correction.
Capture One has this wonderful tool called LCC that can correct any gradual shifts in color or tone across an image so long as you have and additional frame that has the information of the light. Although you may have to go out of your way for this, it will improve your results immensely. What you need is a large - larger than the actual artwork - surface, that is a flat matte gray or white finish edge to edge. I just use a large white canvas that's been stretched, and after I take a shot of the artwork, I remove and replace it with the canvas and without changing any settings at all I take an additional defocused shot. This shot you're going to use LCC on in post and it should end up looking like a flat white plane, you just copy the settings from this image to the actual artwork and voila, even lighting.
If you intend to shoot some artworks in sections (stitching, which at the sizes you mentioned, you'll likely have to), the panel that you use for the shading correction should only have to be as big as the largest section you expect to shoot. Just place the panel in front of that section and take an additional frame for each one. It's important that this panel extends to the very corners of the camera frame in the shot, or else you will get unexpected results with LCC.
What it should look like:
I'll also add that you should set the response curve to "Linear response" under the "Base Characteristics" tab, otherwise the image will look too contrasty and unnatural. Having a linear curve film in the slide film days would have been to die for.
As for the camera... the only real requirements are lots and lots of resolution, and a lens that can deliver the resolution and also have a flat field curvature (absence thereof in other words). The D800E is the ideal candidate for being on a budget, and you'll want the Zeiss 100MP to go with it, but it can be any macro or tilt-shift lens really. Regardless of the size of the painting, you really want to stick to lenses in the 85-135mm focal range for a number of reasons, and shoot at an aperture of around f/6.3 or f/7 max.
In order to align the camera to face the artwork exactly, you may want to have a small mirror with you that you can place near the center of the artwork (if possible) and have the camera look back at itself in the reflection, then you're square-on.
I myself actually use a 5D2 for many of the reproductions I do because the end result will typically be a catalog or small prints (under 30in on the long side), and 21mp is easily enough for that, even as a single shot.
So that's off the top of my head. Good luck!