you can go with the heq5 but the problem will come to light when you load it too much further. eq6 will give you ample movement.
A guide scope can be anything nowdays with sub pixel monitoring. I have used a standard skywatcher 8x50 finderscope (retrofitted to accept a 1 1/4 " nose piece of a DSI) with acceptable results, currently im using a 114mm DSE telescope as a guider and get good enough results for a 20min guide at f 4.7 10" newt and a 40d. Fast iterations on a astro ccd is the best way to run aka .5 second with a DSI 1 (one shot colour is fine) or even lower if you can. this does a great job! good luck if you need any help just post!
