What is the meaning of "vi'Ychalu Es ha'Yamim"?
Radak: The Kohanim will complete the seven days in this way (offering these Korbanos).
From when are the days counted?
Malbim: It is from the first day; it is the seventh day from the second day. It will be explained in Perek 45 that they will begin on Adar 23, and Yom ha'Shemini will be Rosh Chodesh Nisan, just like the eighth day of Moshe's Milu'im was on Rosh Chodesh Nisan.
What will they offer from day eight and onwards?
Radak: Olos and Zevachim (Shelamim), like it says. This includes Temidim, Nedarim and Nedavos and Musafim.
What is the meaning of "v'Ratzisi"?
Rashi: It is an expression of Ratzon (I will be pleased with you). Radak ? there is an Aleph in place of a Yud. The same applies to "Ripinu Es Bavel" (Yirmeyah 51:9). I will be pleased with you via your Korbanos, and your deeds will be pleasing to Me.
Radak citing Targum Yonasan: Your Korbanos will be accepted in front of Me with desire.