No multiplayer of any kind is planned at this time (although I may implement trading if there's a demand for it), and the game is not being balanced for competitive multiplayer
Popular series can vary, but expansions like Sword & Shield, Vivid Voltage, and Shining Fates are often in high demand
Again, the announcement is slim on particulars but uses the elite trainer boxes as an example - those will include one extra booster pack and full-art promotional card as a counterbalance to the increased price
Battlecruiser Magic is often correlated with casual play (since competitive play usually focuses more on synergy and efficiency rather than just big beefy creatures) but that's not a rule
It also has ...And Beyond, which says that whenever this character quests, you may play a card with a cost of two or less for free
I have no doubt in my mind that this will be one of the most opened sets in Magics history