If it is a real Latin word (and it is), the "i" takes on an "ee" sound, so the pronunciation would be
"fee-cuss". That won't stop most people using "fy-cuss".
My problem is about the prononciation of the "cus" part. I know that you read it as "cuss", but in Italian it is pronounced as your "coos" ( and I suppose that it more likely close to the Latin prononciation). So the question becomes: do you want to read ficus thinking of it as an English word or as a Latin one?