Welcome Lu! I'm sure we are all interested to see what you come up with. The Anakin in your avatar photo and the Superman in the Instagram post you linked look very good. I would think that having access to a forum where members can express interest in particular existing or potential products might be a very useful thing for you.
If you are starting out, here are some basic things that I, as a collector/customizer, consider:
Material. Something that I'm sure you will be asked: will your products be cast in PVC or resin?
Necks. Regarding head sculpts, generally speaking, and I think many will agree with me, a neck-less head sculpt is more versatile, as it allows us to use it on any action figure body: if the body does not already have a neck, we can always use a separate neck piece -- that way there are two potential articulation points in the neck -- at the shoulders and at the base of the neck. Yes, I realize that especially with certain bald or very short-haired heads it is visually nice to not have a seam line at the base of the head, but for me personally the articulation is not something I want to sacrifice. Most collectors are not keen on modifying necks, and if the casts are resin, even I am likely to desist -- PVC is more modification-friendly.
Adapters. I'm not certain exactly how your design process works, but if you wish your product to lend itself to easy use for as many people as possible, I would make the hole for the neck peg (and/or adapter) as wide and as deep as possible. Here is why: just reaching into my desk drawer, I pulled out over a dozen neck adapters for male heads that I don't actually use (photo below). They are all basically cylindrical, some of them are flat-topped (with or without a hole), others have a short, recessed round-edged cylindrical top (or something more complex along the same lines). They vary in size: 15-16 mm diameter at the base; 14-20 mm in height. They vary in material, from fairly soft to very hard. For ease and safety of use, the softer the better, no question about that. But it is virtually impossible that you would ever be able to accommodate everyone's preference or need with any single solution. I personally yank out the adapters and use foamies, which provide a reasonably firm fit, allow for adjustment, and easy placement or removal. I realize many would prefer using conventional adapters, but then you are stuck with having to choose between different models. I would suggest you make sure the neck hole is capable of accommodating an adapter with a diameter of a little over 16 mm (the largest I measured, but it probably expands a little when a neck peg goes into it), and a height of well over 20 mm (the tallest I measured). I say well over, because it would be useful for your customers to adjust how high the head sits on the neck peg/adapter -- what is needed or looks best would depend on the body they are using, clothing, accessories, etc. So if one can make the head sit higher or lower as needed, that is always a plus.
The thread linked below does not specifically address the issue of neck adapters as a whole, but it does illustrates some of the issues we commonly deal with when trying to make a head work, and what might be helpful in making a head sculpt as versatile (and therefore useful) as possible.
https://onesixthfigures.forumotion.com/t310-head-conversion-tutorial-updated-with-part-iii-june-2019These are the neck connectors I measured:
This is, of course, my opinion. Others may chime in with more along the same lines, or possibly completely opposite advice. But I hope the discussion will be helpful.
PS I just saw some more of your sculpts on Instagram. Very nice!
