Thanks all for your thoughtful and helpful comments...now that I'm playing more often I can pay better attention. I find that several of my strings often become sharp after the guitar sitting for a day or two - not all, but I haven't really kept records.
Probably my bigger issue is string height - which I know is a trickier nut to crack...I realize I need to have a professional do it. I have to watch some videos on this - I'm willing to do the relatively "easier" parts of a setup - which seems to me to be most of it except taking the neck off...but I realize I need to make sure that the neck does not need to be taken off before I try the other things. I would only try this on my less expensive guitars but I need to watch some how-to videos first, including learning the sequence in which to check things, as well as what tools to acquire. Any tips or links to videos greatly appreciated.
Actually you don't have to have a professional set your string height. A good straightedge to check the neck and fret height to be sure there's no problems with the neck. I took my SG to a luthier to get an idea of the cost to do a couple of things that I felt should be addressed. I was having a slight buzz on a fret on a certain string. Nothing huge but irritating and solvable if I raised the action. He said the neck had a slight curve but was also warped and had a twist in it. Nothing that would render it unplayable and barely perceptible. The frets were worn and installing new frets would go a long way towards getting the guitar back to a "like new" condition. HOWEVER..... isn't there always a "however?" The decorative binding on the side of the neck was cracked in multiple places on both top and bottom and removing it in a good enough condition to replace it would likely be impossible. New binding would not be a color match. The missing neck fret marker would certainly not match the color due to age and yellowing. And the additional work needed on the guitar.... I was wanting to refinish it to it's original factory red...... well, the price was not affordable. Way more then the cost of a new guitar and in the end, he said he really didn't feel comfortable working on the fret job due to the age and condition of the wood and the binding. So, I opted to spend considerably less and bought a new guitar and simply raised the bridge to lose the buzzing. It's certainly playable and with almost no difference in feel.
Then it's a matter of lowering the strings from the bridge which is adjustable in height either as a group or individually depending on the bridge used on the guitar. I'm not a luthier but I have adjusted the string height and intonation on my guitars that are adjustable with good results. I lower the strings until they start to buzz on one of the frets. This will generally be higher on the neck. Once you hit that point, it's the lowest you can go without bottoming the string. So at this point I raise the string until it stops buzzing and then go slightly further to add clearance. Repeat this for all 6 strings. If you have a bridge like I have on my SG.... I have to check all 6 strings to be sure none of them buzz anywhere. I have a bridge that has 2 adjustment screws so I can only raise or lower them as a group with more movement given to the side with the screw that I'm adjusting. It's necessary to check every string on every fret and find that happy medium. Once you have your height set satisfactorily, and the intonation set for the strings, you can move on to adjusting the pickup height and poles assuming you have an electric guitar.
Acoustic guitars often do not have adjustable bridges in the same way that electric guitars do. So if that is the case, you may wish to employ the services of a luthier for that job. My acoustics were fairly decent so I haven't messed with them however, the bridge on them has a removable string saddle that can be filed down. Be very careful when filing because it's not as easy to raise the strings as it is to lower them. A buddy back in the day decided to lower his action on his guitar and ended up having to buy a new saddle and start over.
So... certainly watch a few videos and get an understanding of the job and then decide if you want to tackle it or not.