I've been using a standard tripod, Pentax K30 and either 50mm f1.4 and f1.7 lenses, or 28mm f2.8. Camera has a 12 second timer, I use that to eliminate vibrations from handling it. Also have a remote shutter trigger I can use, normally don't need it. Handy for getting hummingbird shots though, preset the focus and stand a few feet away.
I've tried everything except extremes, my camera does a very good job of limiting noise up to ISO1600, above that it gets iffy, but 3200 at night is acceptable and the 50mm lens can open up to f2 and still do an excellent job. Wide open it's not easy to focus and depth of field is long gone. Then again with star shots, depth of field is not a major issue... biggest problem is most lenses are not sharp wide open as they can be at smaller apertures. I use all manual lenses, the only auto focus I have is the "kit" lens that came with the camera.
I've done a few, but with my lenses, I think it was 5 seconds started to show star trails. At 4 seconds, black dark background and fairly decent star exposure, but nothing like the Milky Way showing like you got. I can't remember the exact settings I used, and I guess my star pictures are on the external hard drive, can't find them, only a few moon shots. Those turn out nice, but the moon is a different story, It's a lot brighter, I can get a good shot at ISO100, f8, 1/500 handheld with a 200mm lens (ancient Vivitar M42 screw mount job) That lens finally went belly up, I'm using a 135mm right now, haven't found another 200mm that will match the old one. I got one 3 years ago, not even close to the sharp pictures the original one got, exact same model lens.
Here's one of the moon shots, 200mm f4 M42 lens, ISO100, 1/500, f8, hand held, taken in June, 2013. I've taken a bunch of these, including several at 1/4 and 3/4 moon. I think a few at half too but those are probably also on the external hard drive. I put them on it because with over 100,000 pictures from the previous camera, Pentax K-x, and so far over 80,000 with this one, I would have run out of hard drive space long ago...So I just keep a portion of the best shots on the computer, the majority are on the external drive.
I had a boatload on Flickr, they decided to limit the number of pictures, and since I had too many I can't even get into my account to cull a few hundred...which reminds me I still need to go find out how to delete the whole account.
Thanks for the info, you brought up some points I had forgotten, since I don't have the equipment to do that I haven't even thought about it in a while. Stacking might be an option but it's not a major photography goal for me, I'm more into nature shots. I had completely forgotten about the tracking setup for a tripod...I've used telescopes with tracking. Mine is a 6 inch Dobson mount, no tracking available so pictures are out. I do a lot of birds, flowers and insects, wildlife whenever I can, and macro shots if I can get an insect or flower to sit still for a couple of minutes. I had a great location for some sunset shots in Louisiana, so far I haven't found anywhere as good around here. Nothing wide open enough unless I take a 30 minute drive. Now and then I'll set up a still life or two.