Here are the Lagoon Nebula and Trifid Nebula: One was with a Televue 101 telescope and the other was with my 200-400 f/4 on the Gem mount. about 2 hours of data stacked in DSS and processed in PS and the wide field 10 minutes of data stacked in DSS and processed in PS
I usually shoot at 800 or 1600 ISO just depends. If in a Orange area where I live 1600 if at a dark site like at our ranch I will shoot 800. You basically want to expose to where the histogram is about a 3rd from the left hand side. So in more light polluted areas can mean a shorter exposure, and dark sites longer. It also helps to get a filter. I have a Astronomik CLS Light Pollution Filter. That helps a lot.
Of course you need a intervolmeter and I would get the Nikon one. I went through two Promaster's and realized you get what you pay for. Luckily my camera store gave me my money back to put towards the Nikon one. Then start testing length of exposure to get the histogram right. Once that is done set the intervolmeter SP? Say 2 minutes then make sure you give 10-15 seconds between shots so second would be set at 2 minutes 10 seconds. Then set how many photos you want to take. Try to get at least an hour, but the more the better. Also set the camera to not review every time, that uses battery.
Then when you are done you need to take Darks. Which are putting the cap over your camera and shooting at the same length. I usually do that when I am packing up. It must be in the same temp as you were shooting. That is to help remove hot pixels and noise when you stack later.