Yes; as the word representing the fourth tone on the diatonic musical scale (do, re, mi) fa is an acceptable Scrabble word.
No, the only two-letter scrabble word starting with R is 'RE'.
Yes. Any word that meets the Scrabble rules is allowed (e.g. allowed and aloud both are acceptable Scrabble words).
No. Cie is not an acceptable Scrabble word.
No. Excelsis is not an acceptable Scrabble word.
No. Viz is not an acceptable Scrabble word.
Abbreviations are not acceptable in Scrabble.
No. Wop is not an acceptable Scrabble word.
Yes. Jo is an acceptable Scrabble word.
No. Fo is not an acceptable Scrabble word.
No. Eariest is not an acceptable Scrabble word.
Yes, "nus" is an acceptable word in Scrabble.