Hi Jowel
The most common criticism of Newt on an EQ mount for photography is they're vulnerable to wind (large surface area) and a bit awkward to balance well. Once you get past the 8" I think these issues really get quite tricky - the engineers are happy to tweak it all, but mere mortals can get frustrated.
For astrophotography, you really don't want to put much more the 10kg on the HEQ5. I'm not a refractor guy, but I think a high quality 4" refractor might come in around 10kg. You'll have lots to learn and figure out before you need to buy other scopes though.
I suggest people have a look at ezystyles website to see what a well set up Newt rig can do:
http://www.ezystyles.com.au/
Or my pics as per link at bottom....
