Nice writeup and thanks for sharing the pictures....
I am also in the process of changing the thermostat too on my 2009 x5 35d with 88000kms.Mine temp stays 73~76 which is not normal operating temp.

Just a side note:I have monitored my DPF regens with BMWHAT app and actually it starts as soon as the engine coolant temp reaches 60 deg. Celsius.But i am not sure about glow plugs remain activated until 75 deg Celsius.But all the documents i read from BMW itself were saying min 75 deg Celsius for DPF regen.I think they changed it to 60 deg later DDE software updates.Mine DDE was last updated in 2012.My bmwhat log is located here:

Bmwhat's app log while regenerating .