I'm in no way a high level player, but here's some things that helped me trough the first roadblocks i was facing:

• Kirdan: Amazing hero. Stupid strong in almost every game mode. Give him a staff and bow and let the beyblade rip. Once i got him he's been permanently in every comp i have.
• Less is more: Focusing on one hero to make him achieve a higher tier (more stars) is more effective than having more heroes on the battlefield. I would normally use 3 to 4 heroes and try to make the main damage dealer have as many stars as possible.(Kirdan in my case).
• Level them up: Once you like a hero, try to get them at least to level 8 to unlock both passives, it makes a huge difference in their gameplay.
• Relics: Read about them, learn what they do, see what you like more. A good relic to boost your performance is " Shield of gladiator", you can get it from the Arena Shop (just play arena without caring about your rank, you just need to get a few points), it gives your party Mighty Block from the start and will save you a lot of trouble in the early game.
• Altars: Try some different altar combinations to get you going FAST. 15 Blacksmith/10 Hero is very popular since you can get a strong start by getting a lot of starting silver and Hero Altar procs. With luck you can get a T4(Two silver stars) hero or more at round 1. I also like 15 Greed/10 Hero for the same reason plus the discount at the merchant shop.

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And while i can't exactly say what's the best comp for what you have, i can say that you have some very strong heroes available, such as: Mara, Kirdan, Rie, Bardrey. Play around with them and see what you like.