Hello there. I'm a fan of Terraria since... 1.2.? I was stoked to hear you guys were getting toys, but over here in Malaysia, Jazwares toys are not readily available. But then again, I admit, I wasn't feeling the toys anyway.
I'm a toy collector. I have a stupidly large collection of all sorts of toys like G.I. Joe, S.H. Figuarts, Transformers, S.I.C., Figma and assorted.
So, talking about Terraria. In my view, 3.75" or 4" or 1/18th scale probably won't really work. At 3.75", you'd be shorter than a lot of current toys in the 1/18th scale market, because Marvel universe pushed everyone to 4". At 4", well, I'm going to assume you guys won't be having super detailed figures like G.I. Joes or S.I.C. Kiwami Tamashii. Instead, you'd probably be something like Bandai of America's Power Rangers at best? And those don't really appeal to the adult collector. They lack both detail and a level of articulation that the modern collector has grown accustomed to.
Now, I love articulation. I'm a toy collector after all. So I'm just not sure I'd dig statues either.
So what WOULD I want? Well, as I sit here writing this, I have a bunch of Halo figures from Mega Bloks on my desk. So why not something like those? 2.5" scale with 12 points of articulation. Balljointed neck (x1), balljointed shoulders (x2), hinged elbows (x2), swivel wrists (x2), swivel waist (x1), balljointed hips (x2) and hinged knees (x2). Now, that might sound like a lot, BUT, what if each segment represents a piece of Terraria Armor? That would allow for a lot of mix and matching, that's in the spirit of Terraria.
In terms of detail, you wouldn't need the level of sculpting and weathering that you'd see on a Halo Mega Bloks. I'd be fine with distinct designs and a flat finish. And I imagine there can be a lot of parts recycling, particularly for the arms and lower torso, since it's not like those have great detail in the game either. Most legs in the game either look like regular legs or bell bottoms. So presumably those can help in reducing the cost. Not to mention, all the recolors/parts recycling you can do in general.
The hands would be similar to what's used in LEGO and Mega Bloks, and would be compatible with those lines. Which means weapons would be cross compatible as well.
For monsters/critters, those I don't mind being regular "statues". But Mega Bloks level minifigs would not only be great for Terraria, but you'd be fulfilling the medieval fantasy niche in that scale.
Just my 2 cents.