In context that he was a foundermember played with is fine to mean he was still a member if wished you could clarify by saying he continued to play with them but it would be a bit longwinded The second Melos bluelink is entirely optional the article isnt long enough to make it really necessary but repeat bluelinks from the intro paragraph into the main text are not uncommon and do sometimes help I cant decide if premiere for the Britten works should be singular or plural A footnote source for the appointments at Michigan would help as this is told on trustIf there is more to add it would be nice to draw the sentences together a little more into two or three paragraphs But these are minutiae quite at your discretion  all is well