hi chris,
i'd recommend getting a HEQ5 equatorial mount. you could in theory put your tube from the dob ontop. or you could get an another imaging newt and it would still be cheaper than getting the 14 goto dob.
i started off doing dob shots some are here
https://www.flickr.com/photos/803366...57634243605994 they were good at the time for a dob but can't compare to an HEQ5 even unguided. mine were taken with the 12" the 14" has a longer FL which will make capture a bit more difficult.
Russ