Can this be worn on a beach?

Yes,This shoes cover the entire foot and have rubber soles. These features are essential for protecting your feet from hot surfaces and sharp objects, such as rocks and shells. Full-coverage, slip-on styles help guard your skin from the sun while keeping sand off your feet.

How much do they weigh?

Size 8 mens pair weighs 12.6 oz

Since this is a narrower toe box, Do these allow for anatomical toe spread and foot contact?

We bought it to so my husband's feet would not slip when he stands up from his wheelchair. He has late-stage Parkinson's. The bottom doesn't stretch at all, and the top part barely stretches at all. The entire sock is very tight and takes a serious effort to get it on and back off. So, it does what we need, but there is definitely no toe wiggle room.

Had no tags or instructions. How to wash and dry these?

It used to be shoe makers always said "don't wash" and some still do. But adhesives have improved vastly over time, and I wash all my shoes periodically. Note this doesn't work well on top-load washers because the shoes tend to float and not really circulate, and can get jammed with the center agitator. It's one of the things I love love love about my front-loader, the shoes come out clean. Just remove insoles (which some sock and minimalist shoes don't have).