How much carbon would be required to remove the Interceptor dose?
between the 25% waterchange and running carbon, most of the interceptor that will be effective will be removed and subsequent waterchanges will finish it off.
- Will the brittle starfish survive the Interceptor? (my reading says he will probably survive)
I'd give him a 50/50 chance. I've lost fromia starfish from the treatment, not sure about the brittle stars. Personally, I'd remove him.
- Will the conchs, Seahare, and urchin be ok?
Conchs and urchin yes, not sure about the seahare, I'd remove him if he's easy enough to catch.
- Will my RBTAs, clams, and Gorgonians be ok with the Interceptor? (my reading says yes)
Yes
- Is this the same dosage everyone else has had success with?
the 23mg tablet are the best bang for your buck. Don't worry about exact dosage, I used about 3/4 of a pill for 220 gal and a half pill for 100 gal. Basically whatever I have left after using little bits of the pill to treat 1-2 gallons for frags. Eric Borneman treated with up to 10x more than DustinDortons dosage with full success.
- Am I missing anything?
Not missing but suggestions. You likely won't have to do a second treatment if you treat longer. I run my treatments between 8 and 12 hours then carbon and waterchange. I try to do the largest waterchange that I can possibly do. The PE you'll see afterwards is pretty incredible and you'll wonder why you didn't notice how bad it was previously 
Don't forget to keep your skimmer running and submerge the air intake.
Great info Stones!! I had printed out most of Eric Bornemans website but lost it and his website is done now, sadly.