What are "Avonos Rishonim"?
Radak: They are the sins of youth. It is as if it says "Avonos Ne'urim."
Radak, based on Ibn Ezra: The sins of our fathers. This is like Yirmeyah said "Avoseinu Chatanu va'Anachnu Avonoseihem Savalnu" (Eichah 5:7). This is based on "Poked Avon Avos Al Banim" (Shemos 20:5), when the children continue in the parents' sins. Do not recall their sins for us - our sins suffice for us!
What is the meaning of "Yekademunu"?
Radak: It is preparation of a matter, and bringing it in front of a person. The same applies to "Asher Lo Kidmu Eschem" (Devarim 23:5).
Malbim: One who is stricken for his sins, they do not have mercy on him, since he is guilty. Therefore, I request that Your mercy precede remembering early sins; if You remember the sins, You will not have mercy. Rather, before You remember them, put Your mercy first, for we are very poor.
Why did he say "Dalonu Me'od"?
Radak: We lack strength to suffer Galus.
