I did not mind the order presented in the textbook.  Here are some comments. 

Unit 1 and 2 have to go in that order because of all the proofs.  Unit 3 they have to prove the sine law so doing it after Unit 1 would be beneficial but not necessary.

Unit 4, 6 and 7 should be done in that order.

Unit 5 is pretty much an independent unit and can be placed really anywhere. 

I liked ending with Unit 8 since it was nice and easy for my students and they loved the Chapter Task with the mouse. 

So those are my suggestions.  Anyone else care to add some thoughts?