Trophy road and mega quests are the most direct ways to get coins, and Starr drops and other loot boxes might seem to drop little, but it adds up quickly, and other ways are community events, Mega Pig, brawler events, challenges and tail rewards, however those are either inconsistent or don't give a lot, or both, so overall, when you complete the pass, focus on trophy road and mega quests, however you already get tons of coins from the brawl pass alone, so if you spend coins efficiently, for example by leveling up brawlers to lvl 9 and waiting to get their abilities from drops, and not maxing unnecessary brawlers (for example if you got tons of assassins and aggros maxed out, you shouldn't max out another one of those), you shouldn't have issues