Nah, it's fine. The lifespan of solid state memory chips are far longer than you'd expect, and likely more than the time you'd use your phone as a daily.
And that depends. Do you favor crisp detail or high-framerates.
If you want crisp details, then absolutely go UHD. Even on displays that aren't UHD, downsampling will help make the benefits noticeable to those. However, if you want silky smooth motion, then 1080p60 is your best bet.
Because your Pixel has unlimited storage for full-res photos and videos, I would suggest UHD.
There's currently no UHD@60FPS option, unless you're willing to splurge on a Panasonic Lumix GH5. XD