(Disclaimer: I’m not a translator.)
Do you want to translate some things in particular? e.g. business contracts vs manga for export.
Each field of translation will have vocab specific to it, even within manga and novels different genres will have their own pools of vocab.
You will get better at what you practice, so if you want to be able to translate manga then you could start practicing translating manga today. I would suggest you start incorporating this practice into your studies this sooner, rather than delaying it until after reaching some JLPT level.
learnnatively.com can help you compare the difficulty of reading different texts.
WK book clubs are a great resource. You can read through books that others are going through (or have already gone through), post your breakdowns and translations, and if you’re lucky get feedback from others or compare to their translations.
I’m currently working through a book from the absolute beginner book club, I and others users often provide translations / breakdowns, and other users may provide feedback.
You can see My (crappy) breakdowns here and here, I was lucky enough to get feedback for both <3.
You can see breakdowns by other users here, here, here, and here.
(NB: If your target translation language isn’t English then this might not be as useful to you.)
If you prepared some breakdowns / translations you should be able to hire a tutor to review them.
It would be hugely beneficial to talk to (many) people already working in translation industry in a role similar to your target role, ask them how they got there, and for advice on how you can get there.