Foreword
There's a big variety of shops available in AFK Journey where you can purchase 
Invite Letter and other summoning currency, 
S-Level and 
A-Level character dupes, Acorns and much more.
To access the shops, you have to visit the Mystical House and then the Emporium. Currently there are 6 available shops here:
- Recruitment Store - contains summoning currency for Banners and Stargaze, Acorns and Soulstones. Refreshes monthly,
- Guild Store - contains summoning currency for Banners and Stargaze, Acorns. You can also buy
Celestial and 
Hypogean dupes from here. Refreshes daily and monthly, - Season Store - Contains Abyssal Essence, EX Equipment Reset (+15), Dream Store currency, Arena Store currency, Cosmetic borders, and S-Level and A-Level dupes for previous rate up banner characters.
- Arena Store - contains S-Level character dupes. Refreshes monthly,
- Dream Store - contains A-Level character dupes. Refreshes monthly,
- Friendship Store - contains Affinity items and Gestures. Refreshes daily.
To learn what to prioritize in each of those shops, check the sections below.
Recruitment Store
Focus on discounted 
Epic Invite Letter and 
Stellar Crystal first and only then buy their non-discounted version. As a F2P player you won't be able to buy anything else, but this depends on how many pulls you will do every month - as the currency required to buy anything here comes from summoning.
Stellar Crystal are required to do pulls on the Stargaze banner as you can't use your Diamonds directly there. So the amount of Stargazing you can do every month is limited.
Important! Stellar Crystal won't appear in the shop until you unlock Stargazing which will require you do to 400 pulls on the other banners.
Guild Store
Always make sure to buy the discounted Invite Letter every day as it only costs you 210 Diamonds (down from 300 originally). As for the monthly part of the shop, get Epic Invite Letter and Stellar Crystal every month.
Stellar Crystal are required to do pulls on the Stargaze banner as you can't use your Diamonds directly there. So the amount of Stargazing you can do every month is limited.
Important! Stellar Crystal won't appear in the shop until you unlock Stargazing which will require you do to 400 pulls on the other banners.
As for the Celestial and Hypogean dupes you can buy here, check our Wishlist guide:
Season Store
The Season store contains characters from the previous season and other goodies. Priority order:
- Abyssal Essence is the priority if you're an endgame player and/or spender as it is equivalent to 500 Twilight Essences, which are hard to come by in high quantities even if you consistently get high ranking rewards from the various gamemodes.
- S-Level characters dupes if you need them,
- A-Level characters dupes if you need them,
- Arena Coins and Dream Store Coins are low priority - you should be able to get enough of them from playing the game daily.
- EX Equipment Reset (+15) is only relevant if you feel you invested your Twilight Essences into the wrong character, but can otherwise be safely skipped
Arena Store
The Arena Store allows you to buy dupes of many S-Level characters dupes and Stellar Crystal.
As a priority, always get Stellar Crystal first - both the weekly and monthly.
There is also the option of purchasing Twilight Essences, but they are so horribly overpriced that they are not worth buying.
Get 1 copy:
Both are one-copy wonders who are able to fulfill their role in the early/mid game with a single copy,
As for the other characters, here's the order and some info about them:
Hewynn is a great Healer who can affect the whole battlefield at the same time. Her only issue is that she's a bit slow and it takes her some time to use her Ultimate, so you often use her together with another Healer early on, such as Rowan, who can speed up her ultimate.
Bryon is a magic Ranger who can summon a Falcon and who focuses on debuffing enemies while killing them quickly. Once you unlock his EX weapon he also gains the ability to revive once per battle. Is popular in PVP for his ability to counter Lily May.
Igor is a hard-to-kill warrior who will survive regular damage as long as he has a tombstone to jump to. Can be used in PVP for stalling tactics as long as the enemy does not have a character who bypasses his brand of invulnerability.
The other characters available have long since been powercrept by better options, and are no longer relevant. Even from the 3 described here, Hewynn and Bryon get the most use, with Igor deserving only an honourable mention.
Dream Store
The Dream Store allows you to buy dupes of many A-Level characters, and Character-Locked temporal essence (That can be turned into universal temporal essence if you have already invested into that character)
For this store, the choice is a bit more complicated as you have different paths based on the direction you want to take your account to and what you want to focus on.
Temporal shards are a trap, and too expensive to ever be worth it.
Temporal essence is of great value if you need it for that specific character, or if you have already invested into that character and just want to convert it into universal temporal essence.
Soul Sigils should be your priority if you use the character and are in need of more dupes.
To learn more about the characters, check our tier list and their profiles for their reviews - this should help you with making your decision. Still, Dream Realm characters should be your priority, because the only way to obtain the currency used in the store is via Dream Realm itself - and if you perform better there, you will gain more currency.
Dream Realm characters:
PVE characters:
PVP characters:
Friendship Store
The Friendship Store uses Pal-Coins as currency, and offers Hero Affinity items and Gestures.
Hero Affinity Items should be your priority as they give the most in the way of tangible benefits (
Diamonds, Invite Letter and Hats).