18" wheels = better performance. Save the $1k and get M3 suspension bits.
And definitely do ED.
I have beige with Montego blue and it is fine. My preference would be for saddle brown, maybe with AW, but I would do the practical thing and get black or beige leatherette.
I like the looks of the 313 with the rest of the 335is trim. But if you can afford them, get lightweight forged rims (Advan RZ-DF, Volks, ...)