It's perfectly normal and natural. My 8 clowns do it fairly often cascading down the tank side one after another. It's playing for them.
if you don't want the snails to be there you can buy a clown loach to eat them
Some caterpillars like circus clown due to wiggling woggling up and down
That's not a good idea at all. The Malawi cichlid will be far more aggressive than other of the other fish and will bully and beat them literally to death. Since both the Malawi and the clown loach like to live at the bottom of the tank and the Malawi will claim a large part of the bottom as his territory, this will lead to guaranteed problems for the poor clown loach. The shark os a little faster and would last a bit longer, but the Malawi would eventually tire him out and kill him as well. As if this weren't enough, the Malawi is from Africa, the shark from Asia (the Pacific rim area) and the clown loach is from South America. They all need quite different water quality parameters to do well at all. You could probably get away with mixing the sharks and the clown loach as they are all reasonably peaceful and wouldn't often cross paths since the loach lives on the bottom and the sharks swim higher in the water column. You'll need a fairly large tank for these species already (at least a 55 gallon tank) but if you have the room you could look into adding large danios, the larger types of gouramis (blue, gold, silver, snakeskin for example) and similar fair sized fish that are not aggressive but are large enough to defend themselves against the sharks if they begin to bully other fish as they sometimes do as they grow up.
It moves up and down.
Two fish. One fish swimming going up an another swimming down.
Yes
Give the clown a raise ($).
You to me are Everything by The Real Thing in 1976. The actual lyric is "Oh baby, oh baby / To you I guess I'm just a clown / Who picks you up each time you're down".
they warm up by being rubbed against the sea anemones and cool down by not really being near the sea anemones
Yes, you are allowed to dress up as a clown for Halloween.
In the average aquarium a sucking loach or Chinese algae eater it's more common name will live around 7 - 10 years, but claims of up to 15 years are not uncommon.
It is just like swimming, up = down, down = up, hold a to pick a direction, take off by shaking.