Excellent choice in getting a Testarossa!
If you plan on doing any wrenching on your TR, I recommend getting a service manual and a parts manual. These are available in book form or on CD from a variety of sources. The manuals will give you "mostly" good information, although there are some occasional discrepancies...so having good mechanical skills, knowledge, and common sense is also a necessity.
As for engine oil, many owners use synthetic 15W50. I have heard of some using 10W40...but I don't recommend that. The TR takes about 14 quarts for an oil change.
That "clatter" your hearing during the first couple of minutes running may be the air injector pump (emissions equipment). This pump injects air into the exhaust stream to help clean up emissions during cold running. The pump's clutch is deactivated after a couple of minutes. Can't say for sure though.....
As for gasoline...the TR has low compression so mid-grade or higher should be fine. I run Shell premium...probably overkill on my part...but oh well.
As for a "tune-up" on a Testarossa...this could be anything from plug and oil changes to fuel injection system adjustments, which requires some special equipment.
One of the major worries for TR owners is the electrical system, mainly the circuits for the fuel pumps, cooling fans, and AC. The main "mother board" located up in the trunk tends to overheat at the white terminal connector strips for those circuits.
The main service job for TRs is the engine-out timing belt service, which should be done approximately every 5 years or 30k miles, which ever occurs first. Also at this time all other suspect items should be replaced, and all fluids changed...etc...etc...
TRs are wonderful cars and can be very reliable when treated right. Black on Black Testarossas are awesome...kinda like Darth Vader on wheels.