1) Now that you have the battle tower, you can ask your trainer to remove all of those points you put into your inventory skill. Because of the chest in the tower, they are literally useless now.
2) Any formulas you give to the Broken Valley enchanter or alchemist will transfer to your Battle Tower people automatically, you don't lose them.
3) I would not bother exploring Orobas Fjords before taking the tower. You're prevented from doing too much there until you get the tower. The only suggestion I have is that once you defeat Amdusias, THEN go to Orobas Fjords and get enough XP to reach the next level before going to Sentinel Island.
When you mind-read the Island on arrival, you gain enough XP to reach the next level.
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Ingredients for enchanting and alchemy are the biggest consumers of inventory space. On subsequent playthroughs, I tend to only pick up the ingredients for enchantments or potions I want that character to use, and sell the rest.
For example, Iron is completely worthless, it's only good for level 1 and 2 enchantments, which are too weak to be worth putting on equipment by the time you can find the enchanter.
Old outdated equipment should be sold as soon as you decide it's not useful. The only old stuff I keep are items with +Wisdom and +Mindread.
Gold in the game is somewhat useful, but mostly for buying unique items from merchants. You can get a lot of gold by using your Battle Tower runners to do diamond farming (but it does cost money to outfit them in the first place).
