I'm beginning to believe that Ingwë should be one of the elf-fathers. I keep returning to this story (it's in The War of the Jewels), and I want to integrate it into our version of Silmarillion. As I understand it, none of the first group of elves, which are called the Minyar in the legend of the elf-fathers, became Avari, so it's within reason to assume that the elf-father Imin (of the Minyar) and Ingwë are one and the same. (Finwë, on the other hand, marries Ingwë's younger close relative Indis later on, and we could assume that he is younger by one generation. Elwë is also of a later generation than the first)
Given that Ingwë is the only Firstborn we know (well, perhaps even The Firstborn), and considered High King of all elves, he should be played by the most regal actor we can find. What do I mean by 'regal'? Well, I don't know... Someone who is a natural leader, I guess, a firm, warm, charismatic person, full of curiosity.