Questions about iPads and pens?

Hi, I want to buy an iPad soon and have a few questions and hope someone can answer some of them.

So, first, what year should the iPad be from at the latest? I don't need the latest model; the main thing is that I can still download typical apps (like Good Notes), etc.

Is every iPad compatible with a pen (including third-party ones)?

What alternatives are there to the Apple Pencil and what should you look out for when choosing such alternatives?

I hope someone can help me, thank you for any help!