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. Excelsis is not an acceptable Scrabble word.
Abbreviations are not acceptable in Scrabble.
No. Viz is not an acceptable Scrabble word.
No. Cie is not an acceptable Scrabble word.
No. Eariest is not an acceptable Scrabble word.
No. Wop is not an acceptable Scrabble word.
No. Fo is not an acceptable Scrabble word.
Yes. Jo is an acceptable Scrabble word.
Yes. Moot is an acceptable Scrabble word.