Timing restrictions based on the card's type are ignored
There is no going bigger than an Omniscience combo kill and that happening reliably on Turn 4 is too strong for Standard
Yes, but only the counters that the planeswalker initially enters with
It will introduce you to the game's rules, inform you about available products, let you know how to find tournaments to play the game in and recommend multiple deck choices to help you compete
These all give you access to powerful removal, counterspell, and protection, something very much appreciated in a deck like Calvary Charge that wants a lot of creatures on the battlefield on your side and little on your opponents'
When a planeswalker is on the battlefield, an opponent can choose which creatures they want to send at the opponent's life total (going face) and which, if any, they want to divert towards the walker