I think it's important to expand on this a little for the new players:

1. Materials without a grade that stack in your inventory do not take up extra spaces. For example, 99 Black Mushrooms only count as 1 item towards your inventory maximum. However, 99 is the maximum stack. If you have 119 Black Mushrooms, they will count as 2 items towards the inventory maximum because you will have one stack of 99 and second stack of 20.

2. Stackable materials WITH a grade will only count towards your inventory maximum if they are different grades. For example, 1x Liquid Aquamarine grade 90 and 1x Liquid Aquamarine grade 89 will count two items towards your inventory maximum. However, 2x Liquid Aquamarine grade 90 only counts as one item towards your inventory maximum. The same is true for seeds. Unless the seed is very rare, combine all of them to grade 100 and sell the one leftover seed.

3. Some specific materials only have one use. For example, all of the base items that are refined into powder and then into salt should only be done so when needed. If you have an Igucite Crystal, Igucite Powder, and Igucite Salt Block, you're using 3 inventory spaces to store, effectively, one item. Keep the base items only, and try not to store their refined counterparts unless you have the space to do it and know you're going to be using the material soon. As another example, if you're making a lot of evolution potions, you can refine Evolution Fruit into Evolution Fruit Juice while you wait for the first potion to finish, but I wouldn't recommend keeping a storage of Evolution Fruit Juice when you aren't making potions. Save room for other things! This also implies that you shouldn't buy basic ingredients until you're going to use them.

Otherwise, very nice!