I think the most important inspiration for him was still language.
Middle-earth isn't just another fantasy world (ignoring the fact that it was one of the first and that Tolkien is actually the founder of "Fantasy"😉 and also not a well-worked adventure story but a linguistical work. It's mostly based on words, words becoming names, names becoming subjects of stories and stories becoming history.
So Finnish and Welsh were perhaps two of the most important inspirations for LoTR, making Tolkien invent own perfect-sounding languages with delicious grammar - and languages of course need someone to speak them.