1)
Why did he say "am I lacking lunatics"?
1.
Radak: Achish's wife was crazy (Shochar Tov 34:1 - and so was his daughter), and screamed and acted crazy inside, and David screamed and acted crazy outside.
2)
What is the meaning of "ha'Zeh Yavo El Beisi"?
1.
Rashi: It is said in astonishment. Therefore there is Chataf Patach under the Hei, and no Dagesh in the Zayin.
