

I mostly agree - however there are physical/mechanical reasons behind the use of some of those. For example, Phillips head screws will ‘cam out’ (driver will slip out of the screw head) rather than get over-torqued, which is useful in various situations - although TIL this was not actually an intentional design feature!
https://en.wikipedia.org/wiki/Cam_out
Hex keys are better than a Robertson (square head) in tight spaces with something like an Allan key, and, in my experience anyway, Robertson can take a fair bit of torque, so they’re great for sinking into softwood - and also for getting out again, even when they’ve been painted over.
Flathead screws, on the other hand, should launched into the sun
Without knowing how serious your relationship is, it’s hard to say.
I would advise not doing this if the main reason is to save money, especially with one person being the sole owner. The power dynamic is too unbalanced.
But if you’re both pretty sure this is a long-term, perhaps lifelong, relationship, then no one here can give you the correct answer. Set aside some time, sit down with your partner, discuss things from both a practical and emotional perspective, do this again in another week or two, and find an arrangement you both feel good about.