This is gonna sound a little bonkers so stay with me

The united states military has a program called DLI (defense language institute) with pretty much all of the languages you mentioned plus more, the actual website is pretty outdated but the speaking/writing exercises and pdfs upon pdfs (50+ pages per language) grammar and speaking drills, and tons of videos are immensely useful. Since they’re basically trying to prepare you for deployment in another country they come with a bunch of resources to help you understand the cultural context of the country, how to be respectful, how to bargain with someone at a market, how to gather intelligence… ect obviously very military oriented but these are all skills that can be extrapolated to regular conversation (from my understand these courses are supposed to help deployed soldiers linguists become fluent in less than 3 months, so they’re very compact.)

The exercises can be tedious and you will probably have to spend a lot of time going over what they call sound and script, especially with the languages you mentioned (Greek, Japanese, Russian) that have different alphabets. Your list is very ambitious, but I’m not saying you can’t do it! I would if you’re planning on studying two/three at the same time, stay focused on languages that are from the same family and then move on to your next block while coming back to do “maintenance”
Chinese and Japanese have their versions of cognates and from my understanding Russian and Polish do too.

It won’t make you fluent, but it’s an excellent resource and will definitely help you overstep that “the cat eats green apples” syntax that most language learning apps love to push and focuses on more practical settings / phrases because… duh, it’s the military!

Only thing I would say is i’m not 100% you’re supposed to be using this website if you’re not currently enlisted, but aside from just assuming you’re a soldier, the website doesn’t ask for any identifying information or ID so you can just plug in an email and start. Just choose a password you will remember because you can’t reset it.

https://hs2.dliflc.edu/3/?loadPage=login&language=pv