95 Ron octane is fine
10w-40 semi synthetic for normal use or if you have a spirited driving style,10w-60 fully synthetic @ 5.5 ltrs for full oil change.
Cambelt is still every72,000 or 5 years but only a fool would take it that far... 56,000 or 4 years maximum seems to be a safe period. A complete tensioner and guide roller change is vital, along with a metal impeller water pump every other belt change if not already replaced. Plastic impeller water pumps tend to crack and slip causing overheating and eventual gasket failure.
If it's been standing and making a rattle on start up it will be the cambelt tensioner, the coil spring inside tends to sieze if left for more than a week. Remove the upper cam cover and look at the tensioner once started, you will notice a little outer peg hopping up and down causing the noise. Turn off and use a long file or flat screwdriver carefully as not to damage the cam belt. Press down firmly and slowly with even pressure on this peg... A healthy tensioner will let the peg move down, a seized spring won't.
Don't put masses of pressure on it as you can inadvertently release the tension by pressing too hard and the belt can go loose on the teeth, it's just a test to confirm the cause of the noise!
Check the tightness of the belt between the top left cam pulley and top idle roller, if it's it has virtually no flex at all, continue to the next paragraph below..... If it has flex of more than 5mm in such a short distance, get it booked in for a belt tensioner change now...
Sometimes all they need is to be used constantly for a few days and presto, the noise disappears, particularly a motorway run of 20+ miles...
Unlike other Alfa engines, the Busso V6 Luke's to be used daily, they don't take kindly to sitting for long periods... They need to be ran.
If it's still giving the same rattle after that, a new belt and tensioner should be changed ASAP or it could snap or release tension without warning at anytime.
You might get away with it.
Best of luck