I've never seen any, which one should I start with and where can I watch them?

since you haven't seen any Ghibli movie I'd recommend my neighbor Totoro, it's a classic and you'll probably recognize Totoro bc it's really famous, if you want something more serious you could go with the boy and the heron or grave of the fireflies

you can find most of them on netflix

ong same, loved your drawing at first sight <3

Thanks. Totoro's design reminds me of Big the cat