New water connection for bathtub in apartment

Hello everyone,

I am new here and not quite sure if I am in the right place.
Here is what I am planning: I am currently searching and have found a huge apartment at a great price.
Now, it used to be a studio and has only a sink and a toilet in the bathroom, probably why it is so cheap.

I can only check the situation on-site on Monday, but I wanted to ask if you think it is possible here to install a new water connection or if it is possible to branch off the sink and then continue with a drywall installation? Or is it better to break open the wall? But how do I find out where the pipes have been laid?
Regarding the drain, I hope that, as in most toilets, there is a floor drain grille and that it might be positioned so conveniently that I could use it for the bathtub, if possible?
Or connect it at the sink or toilet, if possible?

And whether the whole thing could be implemented relatively cost-effectively, or what costs I should expect, excluding only the sanitary work, breaking open tiles, closing, plastering, and reinstalling, etc.

Unfortunately, I don't have any pictures yet; I would provide them later. I just wanted to hear your opinion first.
I understand I need the landlord's approval, a professional to carry out the work, etc.—that is all clear to me. I am just interested in an assessment regarding feasibility and costs.

Thank you in advance!

Best regards
Chris

Pipes can be found, for example, by tapping or with a dowsing rod.

Tapping either directly to find cavities, or putting your ear to the wall while someone taps on the sink. But it's more guessing than anything else.

Or you open up the wall and floor and trace the water pipe backwards.
Can always be reused (including straightening, sanding, etc.) if you know how, otherwise a professional. You just have to work cleanly and repaint afterwards.

I wouldn’t hope for much but rather assume the worst case.

Are you planning to do all this yourself? If not, I would bring the plumber on board right away to see what they have in mind. Possibly get a second opinion as well.

In principle, you can branch off supply lines, provided you have enough pressure in the line.
You can also, in principle, connect into the same drain, provided it is large enough if you run all appliances simultaneously.