Some of your detailing just seems pretty near perfect. For certain repetitive things, like the round rivets on the shield and other spots, do you make a 'stamp' or mold to help keep them uniform?
Sometimes I'll mold and cast multiples of a complicated bit of detail and I sculpt it or something simple like rivets I can stamp in wiht a piece of brass tube of the correct diameter.
Do you make use of rulers and graphing?
Rulers, graph paper compasses,or any mechanical measuring aid is useful esp. in more mechanical subjects like weapons, robots, vehicles,or even symmetrical designs.
I'm not familiar with castilene and styrene, is it like a firm modeling clay?
Castilene is similar to chavent hard but it can be melted down and pour in to molds and worked with a waxer somewhat like a wax.
Styrene is a type of stock plastic that is sold in hobby shops in sheets and tubes rectangular lengths etc and is used y the fabricator the way various sheets and shapes of wood are used by a carpenter. This is used a lot in architectural morels car models , anything mechanical.

Do you start with a brick of your medium and sketch on it what your plans are, or just go freeform?
Either way, depends on how I think it might work best.
Do you often use 3d models to help?
Some times for Movies or tv shows 3D assets are provided ie. outputs of characters, props or portraits. I personally don't like to use them as I'd rather build everything by hand unless they're for visual reference. Everything I'm posting on this site is done by hand.
Many of your works have joints and movable parts.. Do you work on each section individually and then combine them, or work as a whole and cut off the piece to add the joints?. On that note do you take bits off so you can get a better look at the details?
I build and sculpt almost everything separately and then attach or key pieces as need to complete the model. I make articulation joints or complex geometric structures using a lathe and or a mill so that mechanical elements offset organic elements in the sculpture.
Magnifying glasses?
No.
What kind of tools do you use? Do you use any weird tools that aren't part of a normal sculptor's repertoire? Your favorite most used item?
Anything that looks like it might do the job is fair game, wax tools dental tools all manner of knives and blades . About the only things tha are complete bullshit are those little packs of sculpting tools that art stores sell with the plastic scraper, wire and lame shaping tools. I make alot of my tools for specific jobs .

How's your posture?

I keep my seat very low so that the line below my pecs is about even with the table top. This forces me to keep my back straight while I work and reduces neck and back pain.

Music while you work? Certain playlists for certain models?
Sometimes metal progressive or classical, but mostly horror movies and TV shows and I watch alot of football.

What sort of references do you use?
anatomical books, clothing catalogs. weapon books. historical reference; I also have a growing wardrobe of costumes that I model and have myself photographed so I can study the way the fabric falls.

On this particular piece, what made you decide to sculpt in the plaid. Just to give more depth to the fabric?
I like to put in as much detail as possible, particularly elements that most sculptors esp. in my industry would not bother with.

Hope these answers are what you're looking for!

Jean