I believe you're looking for absolute answers in areas where there are very few, if any. Sorry to say.
As with a lot of "bests" this is going to be matter of a lot of personal preference and experimentation to the point where there is really no "best" and the only "best" it can be is what's "best for you."
The Hofner bass already has a vintage sound to it, insofar as it's not a design that is modern/high-tech like some Sadowsky, Zon and other basses. Players have used both roundwound strings, halfwound strings and also flatwound strings on these basses. All of these types are good. None of these string types is going to turn this bass into a high-tech sounding, non-vintage sounding bass. That's about the only absolute here, that I can imagine.
I don't know what strings this bass came with, but more importantly, if you like the tone, then it's good. Keep the strings. When they don't sound good to your ear, take them off. But keep them. Don't cut them off your bass. Pull them out of the back of the bridge and save them for later in case you don't like the new strings you bought, or your taste in tone changes, you'll have the old strings to go back to.
The intervals for string changing depends on your preference in the sound of the string to a large extent, though at some point it may be best to change the strings even if you never want to.
I have basses in which I never have changed the strings, and some basses in which I boil (clean) the strings before every gig. Neither way is right or wrong. It's preference. I prefer both!
Roundwound strings tend to have the most "zing" to them. Flatwounds tend to have the least "zing" and the most muted sound to them. Halfwounds split the difference. I hesitate to say which one is "vintage." Why? John Entwisle (The Who) in those old recordings could be said to have a vintage sound, but that tone is up-front and treble-y. On the other hand, James Jamerson (Marvin Gaye, etc...) has a much more muted tone which is not treble-y, and yet that is a vintage tone as well.
I hope this helps.