Some good points are raised by Noah, as well. However, the length of the exposure is also quite dependant on your sky conditions (light pollution). It's very easy to swamp read noise with short exposures under a very light polluted sky.
In your case, you are right in the middle of the scale (Bortle 5). I shoot from a 5/6 location. 30-45s with a low read noise DSLR (D5300) were not enough to give me a correctly exposed image. Granted, I wasn't guiding - and I haven't tried acquiring images with the C8 even now that I do have an autoguiding setup. Mainly for fear of differential flexure and mirror flop. Also, because I would have to find a way of attaching the guide scope to the C8.
I am more interested in large nebulae, rather than tiny galaxies. So, for now, the 384mm focal length of the refractor is plenty good enough.
That's another thing to take into consideration when thinking about a telescope and the camera to match it. How wide (or narrow) will the field of view be and will the objects you are interested in fit, be cropped too much, or so small that you would be wasting the majority of the sensor?
Telescopius.com is a wonderful resourse. And its Telescope Simulator a tool that does exactly that. Add your choice(s) of camera(s) sensor dimensions, the focal length(s) of the telescope(s) you intend on using, search for some objects and see how big or small they will appear in your final image.
As far as the TS Optics telescope, when I went out looking for an apo triplet, at the end I narrowed down my choice between the TS Optics 80mm f/6 and the Tecnosky SLD 80mm f/6. Both FPL-53, both triplets. The salesperson adviced me on the latter (the store sells both brand and it's not particularly affiliated to a single brand). He said the optics have better quality/treatments and the mechanics are better. I ended up buying the OWL (the upgraded and improved version of the SLD), since the SLD was sold out and discontinued a few days before I placed my order.
I am also based in Italy, so other brands (like William Optics, Stellarvue, etc.) are a lot harder to come by, so the choices are quite limited.
That said, the TS Optics you linked is actually an f/7, so a little "slower" than what I would pick. I actually tried to make my scope as fast as possible, since I bought a 0.8x flattener/reducer (this is another thing you'll need to consider: for a refractor, you need at least a flattener) to bring it to f/4.8. Field of view on most of the objects I am interested in is still quite large, but I gather light faster than f/6.
I guess the price of the telescope increases also due to how fast the system is. The TS Optics f/6 is 2-300 Euros more expensive than the f/7 you cited, despite optics and machanics being almost the same.