Hi Chris,
1. Scope. A fast ED refractor is a good choice, but a reflector is even better.
Current CCD cameras are very good in the blue-violet, as well as going beyond red into infra-red - well beyond what you can see visually at both ends of the spectrum. If you choose a refractor corrected for visual use, images taken with it may not appear so sharp due to the chromatic aberration at these extremes (hence why many DSLR's have a filter to block infra-red). For pure visual use, it would be quite sufficient if the useable range extended only from 440 to 650
nm, but for imaging you'll capture better images - and more photons - in a scope corrected for the spectral range from 420 - 1000 nm.
Fast 6"F8 Cde achromat: 550 - 650 nm
Long 6"F15 CeF achomat: 480 - 650 nm
Fast 6"F9 ED doublet: 450 - 650 nm
Fast 6" fluorite doublet: 420 - 1000 nm
Fast 6" FPL52/53 triplet: 380 - 1000 nm
Fast 6" fluorite triplet: 360 - 1000nm
Better still are reflectors such as the Vixen VC200L
http://www.vixenoptics.com/reflectors/VC200L.htm or the GSO RC Astrographs which offer better achromatism, but there are issues keeping these optics well collimated.
An ED refractor is a good compromise, though.
2. Camera. If you are serious - and I'd say anyone looking to outlay $5K or more on the scope and mount definitely must be - DON'T buy another DSLR. Instead buy an astronomical imager in which the sensor is thermoelectrically cooled, this will give far better results than any DSLR can. The downside is that you will need a laptop to operate the sensor and collect the images. Examples:
QSI 683wsg (see
www.Bintel.com.au)
Orion Parsec 10100C (also from Bintel)
Apogee
http://www.ccd.com/alta.html
Starlight Xpress
http://www.sxccd.com/products
... just to name a few.
In particular look for one that has an internal autoguider capability (some do, many don't), this is used to keep the camera accurately pinpointed on the target to eliminate any drift including:
a) flexure between the optical axis of the camera and the mount,
b) the residual misalignment of the mount on the south celestial pole,
c) periodic errors in the gear train, and
d) atmospheric refraction (effectively modifies the required equatorial tracking rate slightly).
You cannot correct for all these any other way, and a DSLR will not provide the autoguiding function.
Lastly, when choosing the combination of sensor (in a DSLR or one of these imagers) plus telescope, ideally you should choose a sensor in which the spacing of the pixels is well-matched to the focal ratio and the size of the Airy disk of the telescope. Just hooking up a big fat DLSR body to a telescope and hoping for the best is not going to be ideal. For example, if I wanted to shoot deep sky stuff (galaxies and nebulae) with a fast f/4 Newtonian I would choose a rather different sensor than one to use to shoot hi-resolution images of the moon and planets on the back of my f/15 Maksutov.
There are other people here in IIS that can clarify this better.
3. Alternative: if you really want to use a DSLR or an imaging head without the autoguider capability, many amateurs add a small guide telescope to the side of the main imaging telescope, fitted with a cheap autoguider head. Any cheap 80mm refractor will be fine for this, and you can find some autoguiders listed on some of the websites above.
4. Mount. An NEQ6 is on my shopping list too. With most of the Skywatcher mounts (the EQ series) yes you will need a scope mounted on the dovetail to do the initial polar alignment of the mount. The alignment procedure involves a couple of things which you can't do with your camera. Basically the mount is aligned or calibrated by pointing the telescope at two or more bright stars whose positions are known to the guiding system, and for this to work well there are a few assumptions:
a) that the telescope optical axis is accurately perpendicular to the declination axis,
b) that the telescope optical axis is accurately parallel to zero degrees of declination as defined on the dec axis either by a scale, a shaft encoder, or by a physical mark on the mount (often referred to as a "zero position" for most mounts);
c) that the telescope has an eyepiece allowing the chosen stars to be accurately centred in the field of view, ideally to 0.1 degree or so - a magnification around 30X and optionally crosshairs will do fine.
d) ideally, the stars are chosen with 1 low in the east or west (to check the the azimuth of the polar axis) and 1 overhead (to check the altitude of the polar axis)
These are not so easily accomplished with a camera and lens, and even "seeing" a star through a DSLR isn't easy for a star overhead (usually a neckbreaker). You could do this easily by slipping an eyepiece and star diagonal into the back of the refractor, or alternatively add any cheap 60mm refractor on the side.
5. As for other kit...
a) Depending on the optics of the scope you may need a field flattener. Many telescopes have a curved (spherical) focal plane which means that images on a flat sensor may not be perfectly focussed all over the sensor, especially if you are using a large sensor. An image flattener is a lens placed in front of the imager that corrects for this, but you will need to find one that matches your 'scope (buying any flattener at random may make things worse).
b) I'd add a SkyFi unit so the whole lot - camera and mount - can be operated wirelessly from a laptop and/or iPad/iPhone.
