You’re probably fine. You’re aware of attributing material that’s behind what you use — main problems come from people who have never given it a thought. Although laws vary, generally speaking ideas themselves can’t be copyrighted. It’s the expression of the idea that belongs to the person who created it, not the underlying idea. Don’t let it stop you writing. Oh, and join your local collecting society a) they’ll be hot on copyright and have lots of info and b) they’ll pay you money that your work earns through secondary use. Apologies if I’m telling you what you already know — I’m very into this stuff. I wrote about that side here:

Collecting Societies Exist to Boost Your Income