The letters he wrote that are in Scripture now are infallible yes.
2. Was Paul thereby to be considered infallible?
When he wrote the letters that are now Scripture? Yes. Was he always infallible for his entire life? No.
2 Peter 1:21 For the prophecy came not in old time by the will of man: but holy men of God spake as they were moved by the Holy Ghost.
2 Timothy 3:16 every Writing is God-breathed, and profitable for teaching, for conviction, for setting aright, for instruction that is in righteousness,