As is the case with most off airport type operations, there is no "one answer" for most of these questions.
"It depends" applies to most of the questions asked, depending on where, which beaches, what type airplane, etc.
There are some dark sand beaches where huge clumps of bull kelp wash up, get covered by sand, and rot. Leaves an amorphous mass of gelatinous goo, covered by a thin layer of sand. Taxi into that, you you are likely going somewhere you didn't intend to. Possibly on your nose.
Steep beaches work, just be aware that the airplane is going to want to go UPHILL, not downhill as you slow. It is entirely possible and practical to land on some very steep beaches. Curved ones as well.
In some places, you are better off to land up in the dry sand, which implies that you will have to have big tires. And, no, I'm not talking about 8.00 x 6.00 tires. In that stuff, your tailwheel is going to disappear, so be prepared. Three points tend to be very short landings in that case. Sometimes that's good.
Roll your tires on the beach several times prior to landing. This gives you a feel for the surface condition and slope (which is hard to judge), as well as obstacles. Then land IN THE TRACKS you just made. You don't want to pioneer a stretch of beach, verify it's obstacle free, then go land somewhere twenty feet away and hit a stump, rock or soft spot.
Tide tables are a MUST for all float and/or wheel operation near the ocean. Get five copies. Put one in each seat pocket, and one or two on your person.
As to washing your airplane off after it's been on a beach, you can get SOME of the salt off the plane after a beach landing, but you'll not get it all with just water.
But, why did you buy an airplane? Mechanics gotta eat as well, so let er corrode, and support your local mechanic.
MTV