Lefty,
You don't have to purchase an OEM filter but I would recommend it. Your car has the cartridge design I'm guessing so purchasing an aftermarket filter could be hard to find anyway. Secondly, the aluminum washer is replaced every time you remove the pan plug, as you know, as far as torquing goes, just a twist of the wrist and making it snug as you have always done is fine, ( no I don't use my torque wrench for this job). Lastly, you'll have a hard time finding someone who will NOT recommend synthetic oil. All the positive attributes to synthetic oil is well documented, if you can justify the extra cost (and it's considerable), go for it. I use synthetic in all my cars including my '82 240.