3 places where I feel like gender separation doesn't really make sense
Sports
Separation of men and women in sports is fairly admirable as it gives people a chance to showcase their skill that would otherwise be outcompeted. It additionally is nice as women are a group that are often discriminated against and exposure in previously limited areas is nice. However, I don't think that a strict gender separation is really necessary. I think that an ideal system would allow anyone with higher skill to go to the top of their league, relative to the physical ability determined by their genetics. I'm not very into sports, but I get the impression that people's enjoyment often comes more from people's character and effort than the absolute magnitude of their ability. Short v.s. tall people in basketball are one example that comes to mind; a shorter person would require much more skill to reach the same level as a taller person currently. I'm not much of a wrestling person, but I think this is addressed there through weight classes. A possible wider idea is be some meta-classification into classes based on the characteristics that cannot be changed with more practice or other self-improvement.
Bathrooms
this is basically a summary of this very silly 2kliksphilip video
Urinals are more space-efficient than toilets, but typically only are found in men's restrooms. Therefore, with equally sized men's and women's restrooms, the men's restroom gets higher throughput assuming an equally sized demand, and has under-occupied stalls compared to the women's room. Even if both are perfectly sized for average demand, there will still be inefficiencies when outlier groups come in. There's really no reason other than tradition to not just separate out the urinals (if desired) and unify all of the stalls, with full height walls if you think it isn't private enough (Really, as a 6 foot 2 guy, it's silly how low stall wall tops usually are).
Pronouns
I was working on a thing recently and had to refer back to someone in a sentence that already included 2 men. I know that some other languages have primarily gender neutral pronouns, but a concern that I have had is that it would make it harder to tell who someone is talking about. I think there are some alternate systems that are better at resolving general ambiguity though, like having different pronouns for the person most recently named vs. 2nd most recently named, etc. There might be languages that do this already, idk, I just speak English and a teeny bit of Spanish lol. I haven't put all that much thought into this but I'm sure there are ways that could make this problem in communication even easier than it is currently. If we could ever get an opportunity to modify common speech.
If it doesn't come with the 3d printer, a pair of flush cutters is insanely useful. Just be careful with them, especially if you have a cheap pair. Probably wear eye protection.
If you think you would find them useful, there are also filaments at different levels of softness, bounciness, and foaming variants of those. Particularly useful for the soft ones as you can get different levels of softness by changing printing temperature. For any it helps to decrease weight.
For 3D modeling software, Fusion is good but annoying to obtain, Onshape is good but has a non-commercial license for the free version (and makes all of your files public), Freecad is FOSS, decent but not quite as good, Blender is good for detailed or sculpted things that are more art-y (although it's often very difficult to achieve certain shapes that are easy in actual CAD software)
My modelling advice is to keep in mind where supports will go, what places can be bridged, what details the printer can achieve, what axis the vertical should go on (for strength)