I would like to take better photos of the stars, especially the milky way, but my highest ISO setting is 1600. I have now learnt that image stacking can help reduce noise when taken with the same parameters but will it also provide more detail to the final merged image for editing? Ideally I would like to try it out, but we have had weeks of rain and no clear skies, so, hence me asking here first. Also, normally, I would take a 20 to 25 second exposure without stacking, what shorter exposure time would you recommend and also what number of images would be needed to get the best results when using stacking for this purpose?
Yes, image stacking will both reduce noise and let you see more of what's there. In fact, even the Hubble Space Telescope does something like this.
For timing, you can use the rule of 600 (or rule of 400 if you're on a crop sensor), to figure out the maximum length to expose your shots without having trails. Once you know that you can experiment with shorter durations. Obviously, the longer each exposure is, the more light it will collect.
Note that you'll also have to deal with the movement of the stars. I'm not up on my astrophotography software, but you'll need to use some sort of motion tracker to align the images, otherwise you'll end up with star trails combining a bunch of exposures together! (I've used Motion and After Effects for tracking in the past because I happen to have them.) Or you'll need a heliostat or other sky tracking device to mount your camera on.