On the Name Luke

The Latin Lucas and the Greek Leukios would both become Luka (with QOF) in Aramaic, and this would go back into Greek as Loukas.

This is a general rule. In the 1st c. A.D. the Greek diphthong [eu] became [ew] or [ev]. Leukios would have been pronounced Levkios or Lefkios. This shows up in the transcriptions in Aramaic, which have VAV VAV or YOD VAV VAV. Writing a YOD or VAV double shows it represents a consonant, not a vowel. Jastrow does this consistently, and obviously it affects the alphabetical order. However, the mss. are not consistent, and an Aramaic Levka could still be written the same as Luka. The forms with [a] at the end are Samaritan (spelt with HE) or Syriac (spelt with ALEF). Palestinian Jewish Aramaic usually keeps the Greek ending.

The name Lucius became something like Lutchus, Lutsius, and Lushus later on, but not in the period you are concerned with. Assume the original pronunciation of Lukius was still being used.

As said, both Lucas and Lucius will become Loukas in Greek. Regardless of the real etymology, Lucas could be felt to mean forest-dweller, and treated as equivalent to Silva and Sylvester. Lucius means bright or shining, and is related to lux meaning light. I still think you need to eliminate Lucius Flavius Silva as a possibility for the ORIGINAL Luke. Your suggestion of the name having come in when everything was being renamed Lucius is still compatible with an earlier Luke having been the first author. This suggestion of mine will probably come to nothing, but it does need to be looked at and then formally dismissed.