Yes, attackers attacking a Planeswalker can still be blocked by the defender's creatures.
You don't 'defend with' a monster in Yu-Gi-Oh, like you do in Magic the Gathering. The attacking player is the one who chooses what his monster battles against. The defending player does not get a choice in this, he is not able to switch the attack target, unless he has an effect that lets him do so.
To use Rank-Up-Magic Barian Force, you select the Xyz Monster on your field that will be used as an Xyz Material for a Xyz Monster 1 Rank higher than it from your Extra Deck (Must be a "Number C" or "CXyz" that will be Summoned and must have the same type as the monster on the field). Place that Xyz Monster on top of the selected Xyz Monster on the field and any remaining Xyz Materials on the original monster will be added to the new monster. Then the last effect of Barian Force will resolve and take a Xyz Material from your opponent's monster and use it as its own.
Since you don't attack creatures in Magic (you declare attacks, and the opponent may choose to block if he wants) then it's almost a moot point. Technically a Planeswalker could become tapped and be attacked, however the outcome is no different. Nor is there any difference if a creature declares a block, and then becomes tapped.
They do. They go to the graveyard first, and then 'disappear', meaning anything that triggers when a creature is destroyed, will trigger from seeing a token be destroyed.
Isochron Scepter will do this though it will only work for spells with casting cost 2 or less.
No, a planeswalker is not considered a creature in Magic: The Gathering.
No, a planeswalker is not considered a spell in Magic: The Gathering.
Yes, a planeswalker is considered a permanent in Magic: The Gathering.
Yes, a planeswalker is considered a nonland permanent in Magic: The Gathering.
Yes, planeswalker abilities use the stack in Magic: The Gathering.
Yes, a planeswalker can be your commander in a game of Magic: The Gathering if the format allows it, such as in the Commander format.
No, you cannot block with a planeswalker in Magic: The Gathering. They are not creatures and cannot be used to block attacking creatures.
Yes, in the game of Magic: The Gathering, you can target a planeswalker with a spell or ability.
Yes, in the Commander format of Magic: The Gathering, you can use a planeswalker card as your commander.
Yes, planeswalker abilities count as activated abilities in Magic: The Gathering.
Yes, any legendary planeswalker can be used as a commander in a game of Magic: The Gathering.
Yes, a legendary planeswalker can be used as a commander in a game of Magic: The Gathering if the game format allows it.