Casting Traditional casting techniques

Your previous experience with mold making will certainly come in handy. Even if every material has it's own quirks and limitations, much of the basic ideas are the same.

I also prefer physical sculpting. Especially for joints. I need the tactile feedback and the ability to test string whenever I want. I can't imaging having to print a piece over and over to make adjustments, or trying to predict how it will behave in reality when just looking at a screen. I do have great respect for those who can do it, because I certainly can't.

I wish you the best of luck with your project!

Spoiler: Tips for when you start to look into resin casting.

Not sure if this is what you are asking for, exactly, but based of what you wrote here and in the other thread, here are a few tips to get started with resins and silicone. Take it for what it's worth.

Terminology.
Resin, in this context, is the liquid form of a family of plastics. There are many different plastics that can be cast as resins. Polyurethane is the plastic used in the type of BJD that are considered on topic on the main forums here on DoA. Other plastics that can be cast as a resin are epoxy, polyester and acrylic, among others.
So you can say that a BJD is made from resin, and that is true. But it is true in the same sense that cupcakes are made from batter. The finished cupcake is no longer batter and the finished doll is no longer resin. I know a lot of people are very sloppy and careless when they talk about these things, and that's no big deal when just making small talk in a closed hobby space, but when you are getting into purchasing and working with the materials, some of witch are very toxic, it is a big deal. Using the proper names for things are important.

Contamination.
When working with resins and silicone, we rely on chemical reactions. Sometimes, contact with other chemicals can inhibit these reactions or cause things to react in unpredictable way. When using the same work space for a multitude of different materials, it's important to keep things clean and separate.
One common example of this is sulfur. This can inhibit the curing of polyurethane resin, among other things. Sulfur can be found in some modelling clays, in latex, in some acrylic paints etc. Because of this, it's important to keep tools and surfaces clean, certain materials separate and you may have to dedicate some tools to certain materials.

Testing.
This deserves it's own point. You are probably already familiar with this from your previous crafting experiences, but it's extra important when casting plastics. For one thing they are expensive and nobody likes wasting good materials. For another they are often toxic and having to clean up uncured resin or silicone is sticky, messy and not fun at all.
The longer I've been doing this, the less I mind spending the time and materials needed to do proper tests. In the long run it saves time, money, effort and health risks.

MSDS/SDS.
The Material Safety Data Sheet, or Safety Data Sheet, is your friend. Again, you are probably already familiar with this from your previous projects, but because of the toxicity of some of these materials it's very important to save and read these. They contain valuable information that you need in order to know how to safely use and store the stuff.
The data sheet should be available at the shop that sells the product. If not, the maker of the product may also have them available on their own home page. Never use a product that you can't find the data sheet for.
First time you look at one it will read like a foreign language, but just take your time with it. Look up words you don't understand. Cross reference the contents section with filter charts for your mask to figure out what protection you need. These data sheets follow a standard format, if entire sections have "no data" or similar wording on point after point, that usually means that the section is not super relevant to the product.

 

I've done some work with resins, cast foams and silicones in the past and always found Smooth-on products a good starting point. They offer everything from mold making to casting materials and reference which products work well together so it's a good one-stop source. Also their tutorials are really good! I've had problems with unstable curing and stickiness when working with resins before but their stuff felt a bit more foolproof (or maybe I just used their products in a better environment, who knows... but it was easy to get the mix right nevertheless). Not every tutorial mentions it I think but if you're working with very small amounts, weighing gives more accurate results than measuring cups do.


Also I think you probably know all this but still just in case - before you consider casting on your own, make sure you have a safe and ventilated space to do, a mask with the right kind of filters, eye protection, protective clothing etc safety measurements in place. This stuff is can make beautiful things but it is also nasty toxic! After using your mask, put the filters in a ziplock bag and mark the hours worn on it so you can better keep track when to swap them out.

Since you already have moldmaking experience, I'm sure you'll do well with new materials also! Good luck!

 

If you've mostly worked with less toxic materials, it's not super surprising if you never had to read a SDS. They are always good to have, of course, but it's for potentially harmful stuff that they are the most important.

Yes, I can see the attraction of digital sculpting for when someone wants to do many similar thing with just a slight variation, such as small variations in facial expressions etc. But considering the cost of making molds, one would have to have quite a demand for those extra heads for it to make sense from an economic perspective.
And there are ways to duplicate a still workable sculpt with traditional methods too, like the plaster press mold you mentioned, so it's not like digital is the only way of doing that.
At the end of the day, it's just another sculpting medium.

A bit of a personal opinion: Smooth on is not my favorite shop. Their products are all right-ish, but they over prize and over promise. Silly product names and pretty packaging won't benefit your project. They are very good at marketing, though. I will give them that.
When the time comes, shop around.

About mixing by weight vs. volume, most resins are mixed by weight, but there are some that are not. Both parts don't necessarily have the same density so a mix ratio of 1A-1B by weight may not be the same as 1A-1B by volume. It will likely say on the bottle how it should me measured. I agree with coboltconduct that weight does give more exact results, especially in small batches.
Most resins will have a smallest recommended batch size, beyond witch it's very difficult to get a good cast.
The same goes for silicone.