Welcome aboard. Plenty of people here have come back to the hobby after a break of one length or another. Dive in and enjoy and be sure to post some pics.
While I do build other things, I do concentrate on the areas of your interest. There are great, active forums for each of these genre. I like to do an occasional diorama, but most of mine are civil subjects, and these do not fit well in the diorama forum.
I’ve been building for 67 of my 73 years and I build whatever strikes my fancy at the time. I’ve learned a lot on these Forums and am still learning. Enjoy.