as far as I know yes, but be beware that if there are any issues with the I-751 that you cannot overcome, the N-400 will be denied.

yes you can. mostly cases rn 751 is not getting approved fast, they give you a 4y extension. Cases from ppl I know went to the citzenship interview and before the test, they go over your 751 like a interview (you should go with your spouse and all the proofs). If everything is ok, the process to 2nd part that is the civil test

yes apply