It depends on the card and the circumstances, but in many cases yes. Planeswalkers are always very good.
no
I presume that you mean set blocks? Zendikar Block has 6 Planeswalkers Lorwyn Block has 5 Planeswalkers Alara Block has 5 Planeswalkers M10 has 5 Planeswalkers (these are reprints of the Lorwyn Planeswalkers) The best planeswalkers are found in Zendikar Block: Gideon Jura, Jace 2.0, Nissa Revane and Sarkhan the Mad
No.
Rise of the eldrazi
Magic The Gathering - Duels of the Planeswalkers 2014 - 2013 VG was released on: USA: 26 June 2013
no
No, only if you want to play Duels of the Planeswalkers.
Yes, they are treated as permanents, so can be targetted by cards like Vindicate, for example.
Yes, you can have two planeswalkers in play, so long as they do not have the same name or type, otherwise they are subject to the Planeswalker Rule. If you have two planeswalkers with the same name or type both of them most be discarded. You can't have two Planeswalkers with the same 'type', meaning you can't have both Ajani Goldmane and Ajani Vengeant in play - while the two cards have different names, both are 'Planeswalker - Ajani', and would both be destroyed because of it.
A Planeswalker is someone of a sapient species like dragon or vedalken who can traverse the multiverse in the Magic: The Gathering story. Most stories now revolve around these Planeswalkers as they are certainly more powerful than most other characters simply because of their amassed knowledge of other worlds.
No, permanents are cards on the battlefield, ie Enchantments, Artifacts, Creatures and Planeswalkers that have resolved to the field, as well as Token creatures, and Lands.
no, you cannot. you can customize the premade decks with a handful of unlockable cards, but there is no true custom deck building
Attacks may be declared against players, or Planeswalkers. Attacks may not be declared against other creatures. Some creatures or cards have "do x to deal x damage" (i.e. tap to deal one damage to target creature or player). This is different from attacking and you should not confuse the two.