Hi,
You should be able to stack all of them together.
form the Q&A doc:
How many Cisco Catalyst 3850 switches can stack into a single logical entity?
A. Up to 9 Cisco Catalyst 3850 switches can be stacked together to build single logical StackWise-480 switch since Cisco IOS XE Release 3.3.0SE. Prior to Cisco IOS XE Release 3.3.0SE, up to 4 Cisco Catalyst 3850 switches could be stacked together.
If you have 3850-XU (multigigabit) switches or Cisco Catalyst 3850-XS (10G SFP+) switches in the stack, then up to 8 switches can be stacked together to build a single logical StackWise-480 switch.
more info here:
http://www.cisco.com/c/en/us/products/collateral/switches/catalyst-3850-series-switches/qa_c67-722110.html
HTH