Besides the main Store, there are different sections which gradually unlock while progressing in the Campaign. While most of those unlock at the very beginning the Challenger Store unlocks a bit deeper into the story.
As the player progresses through the Campaign the Store improves its supply alongside. The Store can be manually refreshed for 100 Diamonds. The main Store unlocks at stage 2-8.
Mythic Gear becomes available after beating stage 10-22. Then the next Store upgrade is at 21-1, which offers Mythic Tier 1 Gear. Currently, the last store upgrade is at 26-1 and introduces Mythic Tier 2 Gear.
It is recommended by most players to buy the daily Hero's Essence for Gold deal every day, since Hero's Essence becomes the main limiting resource. The amount of offered Hero's Essence increases while progressing in the Campaign but the Hero's Essence to Gold ratio stays the same.
The Guild Stores offer is limited to Gear which gradually upgrades with Campaign progression. Items are bought with Guild Tokens, which can be acquired in Guild Hunts. The offers change daily. The Guild Store can be manually refreshed for 100 Diamonds. The Guild Store is unlocked at stage 2-20.
Legendary+ Gear unlocks at stage 10-22, Mythic Gear at 12-2, Mythic Tier 1 at 21-1 and Mythic Tier 2 at 26-1. A piece of Mythic Gear is priced at around 31k Guild Tokens, while one can get roughly 20k Guild Tokens in 2 weeks if playing in an active Guild.
The Barracks Store offers Rare and Elite Hero Soulstones and four specific rare Heroes. Items here can be bought for Hero Coins, which can be acquired by retiring Heroes.at the Rickety Cart. The offers never change but are refreshing on a monthly basis. The Barracks Store can be manually refreshed for 1000 Diamonds. The Barracks Store is unlocked at stage 1-12.
The best Epic Hero per Hero Coin ratio is offered by Epic Hero Soulstones, since 9 Rare Heroes are required for 1 Epic Hero.
Like the Barracks Store the Labyrinth Store is mostly limited to Hero Soulstones and Heroes, the offer is always the same and refreshes monthly. Additionally Hero's Essence can also be bought here. Labyrinth Tokens can be acquired in the Arcane Labyrinth for winning battles and clearing floors. Red banners give slightly more Labyrinth Tokens than brown banners. The Labyrinth Store can be manually refreshed for 1000 Diamonds. The Labyrinth Store is unlocked at stage 2-4.
While Rare Hero Soulstones offer the best Tokens per Epic Hero ratio Nemora and Shemira are top-tiered heroes that are very powerful throughout the whole game. Many players suggest buying one or even both of them. The options of buying specific Epic Hero Soulstones are very limited. Though buying Hero's Essence in here should be very well considered and probably be an exception.
The Challenger Store offer Epic Hero Soulstones for 14 specific Heroes, including the very hard to get Athalia and Ezizh. The offer is always the same. Refreshing only refreshes the available stocks. However to buy those Heroes one has to use Gladiator Coins, which can be acquired in the Legends' Challenger Tournament. The Challenger Store is unlocked at stage 9-20.