Great post by joemike!
I'll kinda contradict him on one point, though, which is that although Safari 12 uses a bunch of RAM, I"m finding it that it uses significantly less than Safari 11 used...
not that it's particularly faster.
(My green Memory Pressure line is thinner in Mojave than it was in High Sierra, at least in part because of Safari 12.)
I did take down lots of log in items but it still says I'm using almost all my RAM. I have 4 gigs in the old MBP and 8 gigs in the new one of which I am using over 6 gigs of ram at the moment!
You're confusing RAM with your HDD/SSD, Rita. Logs, caches, temporary files, all that sort of stuff is on your drive and doesn't use RAM; if you want to see what's using your RAM, open Activity Monitor and click on the Memory column.
Deleting them will have absolutely NO effect on RAM usage. (And barring some sort of glitch, macOS purges temporary files on its own.)
There are, literally, thousands of files on your Mac with names that sound useless and eminently deletable, but they've all got some sort of purpose, and even if your HDD/SSD is filling up, deleting them is NOT the way to go about freeing up space.
If you need to clear RAM, quit apps that aren't being used and close windows in Safari; if you need to clear drive space, post back for suggestions.
Is there another cleanup app that is free that does a good job? I use OnyX but it never really helped my old MBP. I want to be able to clean out all the trash that I can't tell is trash so that it will run smoothly and not use so much RAM.
Same as before, that "trash" does NOT use RAM, nor does it particularly slow your Mac down unless it somehow gets out of hand.
I haven't used a cleanup app in years, and I'm none the worse for it; I don't even know if they're particularly relevant any more. Among other things, they clear caches which, technically, shouldn't be cleared unless you think one is corrupted, and logs, which, again, barring some sort of glitch, are rotated out by macOS. I'm not sure what more they do, but as I said, no need to know has ever arisen.
Do you like 12? What will I lose from 11 that might tick me off?
I've got no problems with it other than its loading annoyingly slowly, about the same as 11 loaded, but I don't know what might tick you off.
I keep changing my cookie prefs but Safari seems to work best if I accept all cookies from sites I visit.
In Safari 12, you want to keep "Prevent cross-site tracking" checked; I suspect it will eliminate some, if not many, of your undesirable cookies. ("Prevent cross-site tracking", incidentally, is one if the biggest improvements in Safari 12.)
You weren't clear about which pref you've got set in Safari 11, but it may be the reason you've got so many "unknown" cookies.