Should I attempt to represent myself in front of the Orphans Court, on a final accounting objection?

This is really not a good idea. There are certain skills involved in these matters that you clearly do not possess. Remember you are going to be challanging the other side who will have an attorney. Get a probate attorney immediately; you do not know what you are missising.

No, you should not. You may have missed the deadline to make a claim against the Estate. And you are not clear on whether the Personal Representative has objected, or sought a court order dissallowing your claim.

The other answers offer excellent advice. Your question suggests you have some claims based upon an agreement; however, unless you have already timely filed a claim based on that agreement, you will be too late raising such a claim after the final accounting is filed. You had best consult with experienced probate/estate counsel as soon as possible, or risk losing your claim.

I agree with the prior answers and suggest that you consult with counsel before lodging any objections to determine whether you have a basis to object.