Since you want to really learn Spanish first, go with that and become fluent in it since you are already in a solid place with it there.
After that, I would recommend Italian second, since the two languages have similar phonetics and even vocabulary.
Third would be French, since it is a romantic language like Spanish and Italian but is quite different concerning phonics.
German would be 4th. Not an Asian Symbolic language, but still its own beast compared to the core Romantic languages.
Fifth should probably be Korean, and this is because I want to deliberately place Chinese and Japanese together, and Korean is also easier for most native English speakers compared to Chinese and Japanese...at least that what my language "scholar" friends have told me.
Sixth is Chinese. Chinese is all Kanji, which will help you have a backbone with learning Japanese.
Japanese should be last, in my opinion. Japanese is potentially the hardest language for native English speakers, because it takes the Kanji from Chinese, but also changes up the symbols slightly in many regards, and also adds the Hiragana and Katakana alphabets as well. If you study Chinese before Japanese, you'll still have a basic understanding of the Kanji writing system...but Japanese is still very much so its own beast, and is in my humble opinion the hardest major/popular language to learn for English speakers, due to the different vocabulary rules, the thousands of characters you need to learn, and how native English speakers aren't typically used to writing symbols.
Good luck, again haha. I still have a lot to learn about languages, but I am doing my best and it is an interesting subject.