confused about size for for printing

[normie]

I know this questions probably gets asked quite a bit but I am confused by it all.
What is the best page set up if I were to want to print at a maximum of a3 (I usually paint in square sizes).
I use sketch book pro and I am new to art rage.
I don't fully understand the sizing when painting but I had most paintings set to 300dpi, which I recently put up to 800, at 5500px X 5500px. I don't know if that is way too big for my needs (I prefer to be careful) or not.
On art rage it confuses me more, you have page size and print size and dpi (or PPI, that confuses me too lol). The dpi doesn't make things slow but the page size does.
What page size for a decent quality print? I'm sorry if this is an annoying question, I used to the the simplicity of digital painting until sizing came into it :-D thank you