The oil TRs use is specified in the owner's manual as 10W50. The total oil capacity is just over 16 quarts...yes...that's a lot of oil. You can change the oil yourself, just have the proper container or containers to drain the oil into. The oil plugs are large so you get a real gush of oil so be ready. I run synthetic oil in my TR so it's a bit more cost-wise than your average car to change. There are 2 plugs to remove, one for the oil tank and one for the engine. And the oil filter is quite large too, kinda the size that big rig trucks take. You'll probably have to buy your oil filters from a dealer as I don't think there is an aftermarket supplier for them.
As for the single lug wheels, the nut is an 8-sided (octagonal) that is 75mm across the flats. The factory jack kit has a spanner wrench and lead hammer for removing/tightening the bolts. You can buy a socket and big torque wrench to do the job too. I made my own socket and used a large breaker bar at first. But I prefere the factory method better. If your car is in a shop for repair, either remove the wheels yourself or instruct the mechanic on how to do it. It's actaully easy and quick to do. But swinging a lead hammer near the bodywork is risky so you must be careful.
The factory tool kit has various wrenches, screw drivers, and pliers in it. The jack kit has the jack and other tools needed to remove the wheels, and a container with fuses, bulbs, etc. Tool kits are on ebay all the time, but jack kits are harder to find and fairly expensive.
As for octane I run premium usually "just because". But yeah, the compression is only something like 8.7 to 1 so no problems with pre-ignition or knocking. It's amazing the amount of power the engine makes considering the low compression, and only 301 cubic inches in size. I have seen dyno results on two Testarossas and the rear wheel horsepower was 322 on one car and 326 on another. So the factory rating is about right. TRs accelerate quite good considering the final drive ratio is only 3.21. If it were around 4.10 the car would be an animal. I'm quite happy with mine. I had a modified Corvette ZR-1 that was a terror with around 400 horsepower at the wheels and that car was scary fast. But my TR isn't too far off that mark surprisingly. In fact a few months ago I was working on a friends 68 Charger with a 440 six-pack motor. As I was leaving his house in the country....me in the TR, him in the Charger, well you know boys will be boys! We raced from a 10mph roll and he got me at first but as I was reving up in 2nd gear I actually passed him and beat him in the quarter mile by about 2 car lengths! He frantically motioned for me to turn around and go back to his house so we could shoot the sh#t. He just couldn't believe that my Non-Drag-Racer Ferrari beat his 440-6 Charger (neither could I honestly). I was so proud of the ole girl! And the other muscle car guys there were obviously impressed as their mouths were just hanging open.
As far as the weight, TRs tip the scales around 3660 to 3700 pounds. A very heavy car for a sports car, it's really more of a GT car though. But you gotta love 'em! I know I do.