I don't imagine that Big Finish is an issue. IIRC, they have a Time War story coming up soon but the anniversary special is rumoured to cover the same subject. If TV Who wanted to feature a character or do a storyline, I imagine they they'd do it regardless.
I think you're probably right about the second point and I'd agree with you that it's a groundless fear. I remember watching the 5 Doctors as an 11 year old and, even though I'd never seen more than a handful of episodes featuring the first 3 Doctors, I was excited about seeing them (well, two plus Hurndall). Given that the current run has has numerous flashbacks to older Doctors, not least of all in The Name of the Doctor, I would think that fans who've only known the new series wouldn't be in the least bothered by the inclusion of Doctors from the classic show or TV movie.
There are probably fans watching now who don't even remember Eccleston or Tennant, come to think of it!