We don't have any experience of sourcing Darwin stringybark, nor of fair trading considerations, as it is not a major commercial species - at least in the southern States. We assume it will be used unseasoned since a column of any significant size would take quite a while to dry. During the drying process shrinkage is likely to be of the order of 5% (across the grain, negligible lengthwise). It's also advisable to avoid the centre when sawing the log as material close to the centre is inclined to split.

We don't have design data for TTE hybrid products but it's possible Greg Nolan at the University of Tasmania might be able to help. Greg is a professor at the UTAS School of Architecture & Design and you will find more about his background via this link https://discover.utas.edu.au/gregory.nolan. 

Red ironbark is one of the seven timbers that have passed the test in AS/NZS 3837 to be classed as bushfire-resisting and therefore is suitable for external exposed elements up to and including BAL-29 (eg. wall cladding, decking, etc).