With respect to the question of the Avari in Beleriand: a passage in 'Of Dwarves and Men' reads 'It is doubtful if any of the Avari ever reached Beleriand or were actually known to the Numenoreans.' This post-dates the accounts given in Quendi And Eldar, but in any case references from Q&E include...
[u]Sindarin[/u] 'Somewhat later the Sindar became aware of Avari, who had crept in small and secret groups into Beleriand from the South.'
[u]Abarī[/u] 'Such Avari as came into Beleriand were, as has been said, called Morben, or Mornedhel.'
[u]C. The Clan-names, with notes on other names for divisions of the Eldar.[/u] 'The first Avari that the Eldar met again in Beleriand seem to have claimed to be Tatyar,...'
[u]Author's Notes to Quendi and Eldar[/u] 'Eöl was a Mornedhel, and is said to have belonged to the Second Clan (whose representatives among the Eldar were the Ñoldor). [note 33: It is curious that - as in the original text of Maeglin, where he was 'of the kin of Thingol' - in my father's very late work on the story Eöl becomes again 'one of the Eldar' (p. 328), though consumed with hatred of the Ñoldor; whereas here he is a Mornedhel (one of the Avari), and moreover of the aboriginal Second Clan.]
Also (at least with respect to some Avari in Ossiriand), in a note among the Narn papers, concerning the Nandor: 'They had also picked up various Avari before they came back west to Ossiriand.' Christopher Tolkien, Commentary on §38 Grey Annals, WJ
This does not pretend to be exhaustive in any case, just some additional stuff.