I have a couple of fuel system-related questions about my 1980 450sl.

I have had the car for like 4 years, but it has been pretty much just sitting for the last 2. I have driven it a couple of times, but for the most part it is my project car. When it does run, it runs fine, maybe a little bit sluggish, but starts, accelerates, etc etc just fine. However, I do want to go through it and try to clean out the systems as much as possible, a) to make it run better, and b) to reduce the risk of future damage to it.

Question:
1) In terms of the fuel system, what is the extent of what I should do to clean it out? Is it enough to remove the gas tank and clean it out (as well as fix the fuel level indicator), and then just put new gas along with some cleaning agent like Sea Foam or whatnot? Maybe also replace the fuel filter? But beyond that, is there much else I should be concentrating on or that I should take a look at?

2) Speaking beyond the fuel system, what other systems should I pay attention to, before I start doing cosmetic stuff, to get it running nice and reducing future harm?

Thanks for your help!!