Are you building a cylidrical forge And is it for welding? If so The ceramic insulation is pretty ridged stuff so it needs no support to hold it up. About the Itc-100 I wouldent waste it by putting it on the steel "put it on the insulation". About the ceramic tile I really see no need for it unless you are applying Flux for forge welding then it would be a good idea because:
hot flux+ceramic insulation= eventually no insulation..... "the stuff eats it like crazy!"
Hope this helps,
Pj
P.s. If you need any ideas theres bukoo websites including a B.P. on the web http://www.iforgeiron.com/Blueprints_200-300/p2_articleid/223
Look at gos forges at the bottom of the page.