I believe the high iso is to get enough of the light from the not so bright stars, Lisa.
f/4 - for allowing as much light in without messing stuff up - but I would have thought that f/8 or even f/11 would have been sufficient enough.
30 seconds is a good enough length of time with the above settings as not to allow light pollution to ruin a photo.
I have read, and Baz (aka A.S.I.G.N) on here wrote a wonderful thread - https://photography-on-the.net/forum/showthread.php?t=766644 - that if you are in an area with more light pollution - or that you want a "longer" photo, you can stack them - i.e. put the camera on high speed burst mode for 30 seconds at a time or something, using a wired remote, lock it in so it takes something like 2-3 hrs worth of photos, then using special software (that is free and downloadable), it churns it all out and gives you a wonderful photo...



