A post would, yes be boring, your chimney, a far more pleasant story all together.

Hard fasten the hips, ( though it seems to me, this might need be massive or steel reinforced to deal with asymmetrical loads, be they wind or snow ) so they are now tensile members and you have much more freedom to do what you might desire below.

You could perhaps land your hips on dragons in those open areas, on ties in others.

The cant from which you saw the pentagonal posts ( like is often the case ) needs be large for joinery’s sake as much as for load bearing ability. Long story short, wider than the ties/dragon ties, the shoulders are proud of these, and provide full bearing no matter how you join the plates to them.

Seems like a great project you are pulling together…

Be your best and the luck will follow