We love log homes but have nixed them for our retirement house for maint/settling reasons(even though it would look perfect on our mountain lot). So we have decided on a post & beam home, exposed timbers, SIP.
Our house was going to be a 1 1/2 story log home w/shed dormer, two small dormers, full porch- 2000 sq. ft. Instead in addition to beautiful timbers inside, we'll add real wood on the porch posts, front door, anywhere it'll be covered and protected. We thought we'd do a concrete block foundation and cover it(3/4 will be exposed with cultured stone. We want a slate look shingle roof..so that will be lighter than metal.

We're now working on the siding decision. Stucco, vinyl- yuk! Brick...not a mountain look. What about concrete siding? James Hardie makes a rough cedar look plank & shingles (I have a sample and seen a home locally with it and it looks great). It does need to be painted (but paint lasts a really long time). It's not cheap but it is NO MAINTENANCE (unless gets damaged) , no rot, no mildew, no bugs (and fireproof we're in fire suseptible area). Will the timberframe support all the concrete? Anything we need to know about structurally before we decide?

It is common for houses using ONLY sips to be sided with this product so a TF with sips should be ok. I recently restored a house in north texas and used cement board - unfortunately had to remove the original cedar beveled siding as it was too far gone and owner wanted maint-free but not vinyl (understandably). The house was stud construction and those there is a weight difference, no ill effects noted or expected. I found best to use screws vs. nails for install and need to pre-drill near the ends to avoid splitting. You can read more about install of such product from many other sites.
Just my personal thoughts -----> this is your retirement home. How about using natural stone instead - maintenance free and will fit in to your site well - use stone native to your area - a great addition to a TF home.....obviously, cost/benefit tradeoffs to be considered. Option would be stonework on more visible sides with plank on other sides....just suggestions. May your projects be successful.