Would it be possible to increase the number of slots available in your inventory? Also maybe change window size of inventory by dragging the corner or something.
There's no reason to increase the inventory. We're already given max slots without having to buy the expansions. Managing inventory is just a part of the game. Regarding window size, that's connected to the versions/clients. IIRC, the new source has the expandable inventory where you can see all your slots at once.