Just a few suggestions
1) Instead of just upgrading items (For gathering) Have a item shop and give the items differnt propertys and benerfits for example
A certain axe could have a 30% base chance of gathering materials and another 1% for each WClevel whilst another could have a 50% base and an extra 0.5% per level
2) Item levels the more you use a certain tool the better you are with it items could have unique bonuses at milestone levels
3) Give gathering tools level ristrictions it might be a good idea to have 1 universal level to make player use more than 1 skill
4) A sell all button so you can sell all your fish/wood etc at once
5) As well as a sell button you could make a place in inventory button materials in the inventory can be used to upgrade your house it would encourage people to use many differnt skills
I hope you continue updating this game :)
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These are some great ideas! Thank you!