If you want a mechanical keyboard, you should probably carry your own, as even the "mechanical" keyboards on laptops like the Eluktronics Mech 15 are IMO pretty lackluster. The NuPhy Air 75 fits exactly over the keyboard deck, btw, so that'd be my recommendation (replaced an Anne Pro I was using, which felt better, but was much bulkier. A Keychron low-profile might work as well, but I can't confirm whether it'll sit on the deck properly or not w/o having to disable the built-in keyboard.

In terms of the built-in keyboard feel, it's adequate. I would say that it reminds me of the keyboards on early-2000s Apple TiBooks. For the previous gen (and in my copy as well) there were reports of slight unevenness of the keyboard deck, although it was more of a curiousity than an actual issue in day-to-day use.

I don't know how high refresh rate displays affect battery life, but in the worst case I imagine you could turn down the refresh rate when you aren't interested in using it (certainly refresh rate is tunable in X11).