Ice_heart... trading for people with over 100 victories would be unfair, some don´t win that much and it still could be cheated, the cheater just creates 3 accounts, picks starters and puts them to fight each other from his computer and laptop for example, until both got 100 wins and losses, then gives the starter cards away, don´t underestaminate cheaters because they can and they will use every single lame way to cheat their ass off to look "better" than others.
Turn timer isn´t too long, some people need time to think, and if they don´t press anything for long enough time it starts the countdown for you, some can really try to piss you off by waiting almost minute before pressing their move, but you just have to deal with it.
Trading cards can´t be added...
People would to new accounts, pick different starters and trade them to their main accounts.
There simply couldn´t be working solution to trading cards without someone somehow exploiting it.
Kylas, survival is with 4 chars, all level 10 and starting gear, but you can give them stats, skills and buy gear (you got lots of starting money) before going against endless waves. Better have 2-3 healing abilities and at least 2 resurrects.
Dudes... You got wrong strategy if 1 miss makes you lose the game, only place where it should screw you up is both at 1Hp, you´re faster but you miss... No other cases. Period.
I don´t think everyone having cornelius is anyhow saddening... You just have to figure ways to counter him, and i personally use him because i see him being better than Cain Solomon.
The strategy in the game is to know when enemy switches out... And if you hate switch fights, do something about it.
I don´t think a card "shop" would be good. But weekly challenges give a random card (either random item or random character, otherwise all would be whining because they only get crappy items) might work.
 "Kongai"){kind=icon}
 "Monsters' Den: Book of Dread"){kind=icon}
 "Pandemic 2"){kind=icon}