As I experienced, the main source of frustration in this game comes from trying challenges way above the level of the cards available to you. Your pool is enough to farm AI3, but it's hardly par with AI4. As others suggested, farm AI3 for a while and also try Bronze arena (many 1 HP decks there grant you an easy quick victory). Once you gathered enough cards (either bought from the market or won, you might move up a level. Don't rush toward the top or you will get soon too frustrated to play anymore and you'll just give up.
The Community-recommended decks section of this forum is a great place to start looking for ideas, but the best choices are those tested in the "Farming studies and statistics" sub-forum of the General Discussions section. Before putting together your own decks play for a while with other people ideas and then you will make enough experience to make your own mind.