While there are a handful of rares that are worth more than the $10 pack, apart from Rishadan Port, most of these rares just sneak past the $10 mark, which means the packs where you open a "good" rare won't typically be enough to cover for the packs where you open a bad rare
The rules of the game are streamlined so that new players can pick it up quickly, but the cards will have nuances that allow for deeper strategic elements, especially in the building of decks, that give the game more depth for advanced players
Modular Monstrosity loses all the keyword abilities you've chosen so far, as well as any other keywords it picked up in other ways
Secret Tunnel looks like a direct replacement for Rogue's Passage, but hold on there, tiger
Theres no maximum deck size, as long as you can shuffle your deck in your hands unassisted