So I’ve been studying if you can call it that two languages on Duolingo.
I’m at level 7 in Spanish and level 2 in Italian. Many similarities between the two languages. As I mentioned earlier Italian seems to lean more toward modern Latin, whereas Spanish has that plus influence of Arabic and other language and culture.
Spewing Truth in the face of Lies 
I read this post and the one from the day before. I love these comments about the roots of the languages. I see your plan is to learn five languages and that your next one is Portuguese, and then maybe French.
I’m wondering, why not learn some language that is totally different from these Latin-rooted languages? None of my business. Just wishful thinking on my part but I think this is what I’d want to do if I were that good at languages. I’m good but never learned more than my mother-tongue, which is Pennsylvania German/Dutch, English, and Martin Luther’s High German Bible. I grew up learning those. I’m also learning to read some modern German via websites.
I’ve tried learning Spanish but never got beyond the first couple classes. The same for German. This was all at the university level. Seems I learn best by exposure. Let’s see, I did pass an ancient Greek language university course, though I’ve forgotten most of it.
Ah ok – all of the Latin based languages use the same vowel set. One of the things throwing me on studying Spanish again is I know it’s definitely not Castillian Spanish.