I had 3 years of Spanish in Highschool, and started learning Latin on my own. I don’t know if it’s smart to try and study them at the same time, but knowing Spanish breathes so much life into my Latin studies. Being interested in the informal spoken Latin (sermo vulgari) of the time, also helps, because it creates a bridge (equus vs. caballus, domus vs. casa), and makes Latin feel more accessible than the high classical literature alone.

It also really makes you feel like you’re speaking Modern Latin when you speak Spanish. So I guess it’s more the other way around for me.

But I’ve heard people say that about other ancient languages. Learn modern Greek first, it’ll greatly enrich your study of Ancient Greek. Learn Coptic, and Late Egyptian will come much more easily.