I use the EQ6-R Pro mount, was my first as well. Its very solid, and easy to use/learn. Highly recommend!
Regarding the guiding.....I am of the camp that says "it can wait". I am new to the hobby (6months), but I view it like this. You want to race a car, do you buy a turbo charged 650hp McLaren Spider? No, you start small, learn and grow. A lot of advise I find around the site here needs some of that filter. Guiding is NICE to have, it is not required. Turbo is nice, but gas is required. Guiding helps, but if you cant get the basics under control, guiding is just another layer of frustration, you could spend nights fighting your guide camera when the problem is somewhere else in the rig. Another optic, another camera, another cable, another program.
I have no guidance system (YET), never have. But I am leaning towards getting one when my budget allows. I take 2min subs without issue and have done some sampling at longer exposures that turned out fair. My scope's FL is 480mm, your longest is 600mm. Ball park closeness. I would venture that you could take plenty of images without the need for guidance with that 600mm lens. With the wider field lenses....you will be fine without guiding getting started.
I am not against guiding, just think its a "when you grow into it" kinda thing. There is no "gotcha" if you dont buy the guide gear up front. You arent missing out, or setting yourself up for double the expense later. Everything you will need to add guidance to your setup now, will be the same later on.
Take a look at this site for imaging ideas. https://telescopius.com/ (formerly Deep Sky Object Browser) Plug in your FL and camera dimensions and it will give you a decent idea how an object will fit the frame. Bear in mind the "map" is a sky survey, your image will not look like that, but the size and framing will.
Newtonians (or most scopes) for visual use, and for photographic use are not interchangable. Size of the Secondary, how far the focal plane sits outside the tube, vignetting, sensor sizes, and a myriad of other challenges come into play. Astrographs (newts for photos) are specially designed for this work. Also, the 1600mm FL is a tougher place to cut your teeth, doable yes, but again, its about the journey.
I bought this adapater to clamp my DSLR direct to the mount, also needed a 3/8" to 1/4" screw adapter (tripod mount screw to camera body size) YMMV
Im sure you can find an equivelent selection in NZ