Oh wow. I knew joining this forum was a good plan, you've all given so many great ideas and references. xD I'm glad people are playing around with it too, hopefully that means it'll also capture the inaginations of my players. Or maybe they'll just go there to shop and ignore everything else, who knows. Haha.
I'll see if I can track down the sharminds and undying court lore when I get a free minute. World building is fun but I'm sure pouring a lot of time into it! I've decided the players, in an early game while I'm still railroading a little, will come accross an old wandering construct who will lament that an area that was 'recently' endless greenery is now deforested and covered in ice. This is to fireshadow an unrelated event for months down tthe road, though if he goes to investigate it the players may later find his corpse there. Beyond that meeting the rest probably wony come up for a little while so I'll save the details for then, but a ritual sounds good. I'm not too worried about increasing numbers because of wars and also that 10,000 years of adding a ruler every 150 years with none of them ever dying still only gives about 70 constructs - a smaller upper level than many modern systems of rule. Individuals getting bored needs consideration though... I like the 'children of stone' idea and really like the 'book of stone', but I may save them for another race later on in the campaign.
Thank you all for all your ideas and feedback. As a new player this is really valuable to me, and makes the game much more accessable.