Have raw lobster once a year. Realistically speaking, it's far less nutrient-dense than raw oysters, and you get not that much meat per lobster. The lobster eggs, though, taste great.
I found raw scallops to taste wonderful, being very nutrient-dense too imo, but they are usually viewed as being too expensive by others. I find spending 20 pounds sterling on 20 large raw scallops is well worth it, though.
I have no idea re opening clams. I tried and more or less gave up. That is, I eventually used a hammer and picked the tiny bits of flesh out from the shards.
Oysters are easy to open. Just buy an oyster-knife(I got mine from amazon, as I recall). Try to force the tip of the oyster-knife into the front end of the oyster on the side, and once it's in, twist it round to get the shell open so that you can force the upper shell back and tear it off from the lower shell. Then hack at the hard, round, white muscle to get the softer oyster parts off and gulp them down. If you don't like the salty taste, you can do what I do with raw mussels, which is put the oyster-flesh all into a pint-sized glass, , put your hand over the top of the glass, and then turn the glass upside down for the liquid to run out.
