You're the kind of people I count on when I'm making this mod. As the creator, its often hard to catch every little thing I mess up on such as money exploits, incorrect damage and useless items. So when someone such as yourself gives me a large list of things that need some work, with valid reasoning, it makes my job much easier. I'll try to explain and tell you what I've done for some of the problems.
1.Yep, it seems I put the wrong value for the invis cloak, it definitely shouldn't be 1 gold, so I've set it back to the proper 5 silver.
2. I've increased the price of the boss summoning items to better equal the amount of gold you would get total from one of the fights. I've also made an item drop from the Beholder that will alert the Zombie to move in. (good idea)
3. While its true the Mech weapons are broken beyond belief, that was almost my intention. But I've since then retracted on that idea and properly nerfed them. Twin's Ire only hits the same target 4 times now and the Destroyers Rage has a much longer use time.
4. Darksteel in the next update will be much easier to craft as I've changed the recipe around. the old componets, minus the darksteel cores, will now make a Darksteel Ingot. Ingots mixed with the cores will make the items, so you'll need less darksteel cores over all. Life Leech and Soul Siphon also no longer require Darksteel Cores, Just the ingots.
5. I might...
6. I'll have to check on the money exploit with the Weapon Master
7. Its true that early hardmode is about being able to do any damage at all. Which is something I hadnt thought about when making the armor. I've changed its effects around with that in mind. The total decreased damage has been decreased to only 10%. With that, the Set now gives 20% increased damage( meaning +10% magic damage in the end), 50% decreased mana usage and a buff that will occasionally summon mana stealing orbs. These orbs seek out enemies and when they hit them, they'll return 15 mana.
8. All of the hardmode staffs are getting a rework, so dont worry about that.
9. As of now, with r15, Minions don't work. But I have found a major problem with my summoning staffs which had been the reasoning for their rapid attack patterns, crazy movements and all around confusing knockback. As of now, they function properly and aren't cocaine fueled monsters.
10. I might need to buff Life Bloom armor a little, but with that buff, I might need to make it slightly harder to get. I'll think on it. I might also add combined summoner accessories, that doesn't sound like a bad idea at all.
11. Turns out a lot of my projectiles were doing magic damage...
How silly of me, its been fixed though.
12. I've buffed the thorium revolver on the off chance someone might pick it up. Way faster use time, more damage.
13. I wouldn't know how to fix that at the moment, I'll look into it.
14. That brings up an interesting point that I might need to explain. When I started making the Thorium mod, my goal in mind was to have more options for every path a player might take as well as offer some fun stuff for multiple players at once. A lot of times in multiplayer, at the start, your group might work towards getting one of your friends copper armor over time. So now that player has better armor than you, now what? Well with the Thorium mod, those other poor saps can have Sandstone, Frost or even silk armor. That way no one ever feels unspecial amongst a group with everyone having the exact same armor. This goes for hardmode too, someone can have mythril, while another friend has Dragon or Flesh or White Knight. Then you can have a friend with LodeStone, Valadium or Hallow. Its all about giving the players more options.
15. I'm a little nervous about adding different prefixes. I would end up making an ungodly powerful prefix my accident.
16. I can definitely add meteorite to his shop.
17. Might be a little hard, but I'll try.
18. No, hes pre hardmode... Maybe you're unlucky? Checking his Spawn conditions, he should be appearing.
All in all, I would say your post has helped me significantly. I'll throw you some credit for your balance contributions.