Superb work so far, happy to see fellow DIY metal casters here. I see that you have experience with what is possible with gravity casting and where the limitations are – I think you nailed the level of detail for the intermediate sculpts. If you are interested, I have documented my journey in this thread.
What material do you use for moulding? I have used HTV rubber so far which is excellent but unfortunately very hard to come by where I live. And which alloy is this? Looks similar to the one I used (Sn95Sb4Cu1: 95% tin, 4% antimony, 1% copper).