My own $0.02 on your list of questions. My assumption is that you are trying to stretch a budget.
Camera: The 5D Mark III is a great camera. A refurb will help you save money. You can often find it new for less than $3000 using CanonPriceWatch, so make sure the refurb is discounted below that.
Lenses: For video only, you probably can't go wrong with Canon, Rokinon, Tamron, or Zeiss. I have at least one of each, except for Rokinon (and they seem to have a good bang for the buck). I have bought my Zeiss lenses used from LensRentals and saved quite a bit. I doubt I'll buy another lens new. Don't overlook the non-L primes from Canon. I have the 50mm 1.4 and it is very good. It is about the shame sharpness as my Zeiss 50mm 1.4. I just like the look of Zeiss, so I prefer it. Also, for video, the manual focus operation of Zeiss lenses is much nicer than even Canon L lenses. On operation, the Rokinon Cine lenses are worth a look. Don't go too crazy here. You can only use one lens at a time! I strongly prefer primes. For interviews, a 50mm (on the crop sensor 60D or the full frame 5D Mark III) is nice, as is an 85mm (on a full frame). The 50mm 1.8 would do great for interviews on a 5D Mark III, especially once you stop down a few.
Loupe/Monitor: Axilrod mentioned the LCDVF. I love mine. Best accessory I have!
ND: A variable ND is handy. I've found it to be great in some circumstances and hit-or-miss in others (in terms of negatively affecting the image quality). I find the image quality to be better with fixed ND's. Consider a set of 0.6-1.2 ND (I have Tiffens). Get one set based on the largest filter ring you need (probably 77mm or 82mm), then get cheap step-down rings to adapt to smaller filter sizes. You might then need a cheap flexible screw-on hood, too. You can stack fixed ND's, which is what I find myself doing when I don't need the flexibility of the variable ND.
Slider: I don't have one. Sometimes I want one, but not very often. Might be different if I had one. I do have a skate-dolly (DIY slider). Nice effect, but for interviews, I don't find it critical.
Lights: I would put this as the first priority if you don't have any. Look for sales on 3-light kits at B&H or Adorama. You don't need to spend a fortune on lights, but some money spent on lights probably has a larger impact on the overall image more than the upgrading the camera or lenses that you already have. Good lighting will go farther in making your shot look professional than upgrading your other equipment.
Monopod: I have one. Used it sometimes. Haven't used it much recently. With the LCDVF, I get a lot of stabilization from having contact with my head. When I need more, I prefer a tripod. It is handy if you are moving your position (where you stand) a lot. Likewise, I have a rig. What I love about DSLRs is that people don't get freaked out by them the way they do a video camera. A rig ruins that. Sometimes a rig is great. If you are doing a lot of pro handheld, then you need it. If you are doing set shots, a tripod is often the way to go.
Tripod: You definitely need a video, fluid-head tripod. This is a fairly expensive item ($500+), but worth it.
Follow Focus: I don't have one. Sometimes, I wish I did. You can get by just using the focus ring on the lens. This is definitely a "nice to have" item.