I hear you about the time commitment.
It would be helpful to enter your car in the lotus-europa.com registry as well as the Lotus registry with andy graham (agraham@lotuscars.com).
I suspect that the oil leak is from the rubber drain between the head and the block under and towards the rear of the carbs and the oil is dripping on the exhaust pipe on that side of the motor. I understand that it can be replaced without taking the head off.
I have a stock cooling fan I'll let go cheap, but I think the best solution is to get an aluminum radiator (available on ebay) and a good modern fan. It sounds like your motor just needs some tuning. I recommend Pertronix ignition (available from amazon) but there's nothing wrong with the standard points and condenser.
I don't know what kind of sealant the PO put on the gas tank, but unless cost is a huge issue, I would advise getting alloy tanks. Short of that, I'd get them welded up properly and in a way that water doesn't collect on the top of them. The rear drums aren't really any different from most drum brakes. They should drag a tiny bit. The parking may have been set. I'm not sure why else the car would slow down so quickly when put in neutral. The electric fuel pump is a good addition. I would also make sure that the plastic 'T' between the carbs is replaced. The air box is just bolted on to the face of the carbs. I think there are also gaskets that go between the carbs and the air box.
You can get an idea of the condition of the frame by looking at the bottom, check the condition of the frame by looking at it along the engine and you can get a bit of a view by looking in front of the engine into the 'Y' of the frame. Also, if you can, take off the elbow rest and look into the frame there. Poking around in the front - maybe take off the bottom plate between the 'T' and the nose of the car.
The body seems pretty decent. Mirrors are available - the Mach 1 Sebring mirrors are a match. The mirror covers were originally made of chrome plated pot metal or zinc but now they are plastic. If you don't like the plastic covers, I bet you can swap the mirrors from the new ones into your mirror covers.
Windscreens are available.
There are reproduction crash pads, console covers, and dashes.
The tach is probably reparable. I'll bet you can get a replacement, too.
There are a few places to look at for sloppy shift linkage. The bushings at the bottom of the shift lever where the forward end of the linkage attaches. If you have a 5-speed, there is a bushing near the engine/bell housing area that could need to be replace, and there are u-joints between the front and rear shift links and at the tranny shift shaft and the rear shift link. Those parts are available.
I think your stocks will behave for at least the short term. I don't know anything about owning an Evora or an Elise, but the Europa is a very simple car. I wouldn't be intimidated by it. After all, I built one. If I can do it, anybody can!
Good luck and keep us informed!