Some here seem to recommend ANKI or SRS and I would like to add maybe find some Taiwanese Manga, Light Novels and novels of subjects you like. This of course I mean scaled to your level. In the process of reading these I truly think it will help speed you up.

I don't know how Chinese characters are with Chinese only Japanese. Can radicals also help speed up your understanding the further along you are...is curious.

It's a different language but it took me about 6 years to start reading Japanese books without feeling like a total noob. Everyone's different for sure. I started Japanese at age 34. I think if you're younger you can pick this stuff up faster.

what's "to pick up?" . I mean if you're just studying characters, their independent meaning and pronounciation, depending on your pace you could do 1000 in a month with the right materials. I did around 2.8-3k kanji with heisig and some other tools in around 5 months I think.

But then there's still actual vocab, compound words, context, slang etc

I'd try to get to as many characters as I can with something like heisig or similar tools in +/- 2 or 3 months and then focus on reading in context.

My experience is centered around JP though, not entirely the same..

In 1 year I learned 1000 as a backseat thing, but you say you are maintaining 10 other languages depending on what this means this could make it take forever lol. Could you elaborate on what you mean by 10 languages and what constitutes maintaining them?

Anybody have personal experiences with retaining the Chinese symbols?

Just to recognize them? I would imagine just a few months. for french it took just over a 2 months. I understand Chinese is different, but if you are really going at it, @LuckieNoob's idea of 4-5 months sounds about right.

If you manage to learn only one character every day roughly 3 years. If you learn 10 every day 4-5 months.

Just divide 1000 / characters you can learn per day.