The ending doesn't really answers, or even attempts to answer, the questions implied about having a near-human robot as a lover.
It just ends with a timeskip and an admission by Chika that she loves Hiro after all and that it's normal.
What about when she grows much older? As Hiro is a very expensive machine, she's not going to see her often. And the researchers are under no obligation to keep her running. How does that affect their relationship? That to other peope, Hiro is just "a thing". One thing is for sure is that they can't get "physical". So Chika is going to go full abstinence? Or have a human lover on the side? Maybe to have kids?
I'm just frustrated because there's too many loose ends. If you bother to make a plot about a love story between a robot and a human, then you better see it through, until death do them part.
I can't answer most of your questions, but there's one in particular that we know the answer for:
What about when she grows much older? As Hiro is a very expensive machine, she's not going to see her often. And the researchers are under no obligation to keep her running. How does that affect their relationship?
We've hear the answer for this from Praha's creator. He said he hopes "Acchan" serves as a stand-by person for when humanity is no more, which means the objetive of Praha's whole investigation is most likely towards self sustainability.
We also know Hiro was asked to think about no longer having those she cares about with her, and we've seen the process she undertook when her "father" died. So we most likely can infer what will happen when Chika is no more. We know Hiro makes "tags" specifically for those she cares about and the things they care about, so it's very possible "her heart will go on" once Chika is no more.
Also, Chika seems very aware about the whole "immortal robot" thing, even at 16, so we can guess at 27 she's more aware of it.
Also, why not Chika having a lover? I'm pretty sure, with the right amount of information, Hiro would conclude that's the more logical course of action