I'd get 15 sq ft minimum (3ftx5ft) Better have some extra than running short, and I don't have much extra. I suggest you get a little more if it's your first time.
The crack IS visible
Have a pic of your E46 with said trim?

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00 E39 DINAN S1 //M5 (82k miles)
06 E53 DINAN 4.8iS, born 2/18/2006 (126k miles) http://www.xoutpost.com/bmw-sav-foru...s-my-dslr.html
90 Straman Z32 TwinTurbo Convertible, (1 of 44 ever made) 5 speed, 444rwhp/451rwtq
01 360 Novitec Spider F1 (26k miles)