just bought 5ltrs 10/40 valvoline from ecp, came to 12 quid free delivery.
i had previously used the ecp branded 5 / 40 as advised by fiat, but it sounds a bit tappety so im going up to 10/40, for whatever difference it will make. 10/40 is also ok in fiats books and its also what ive always used in other vehicles.
last time i changed oil i got just over 4 litres out of it, the sump holds 5ltr.
are you buying a new sump plug? i haven't, last time and first time i opened it, it snapped my allen key ( socket type) being on so tight. i suspect it always to have been syphoned out with a pump through the dipstick by the previous owner, maybe the sump plug had not been opened in several years, if ever.