1.Can we stack 2*ws-c3850-24T-E withws-c3850-12s-e? Yes. see link below
StackWise-480 supports a mixed stack of any Catalyst 3850 models (48 ports 10/100/1000, 24 ports 10/100/1000, and 12/24 Ethernet SFP ports; see Figure 1). You can mix the switches with different number of access ports (48, 24, and 12), different type of access ports (copper and fiber, PoE, and non-PoE-capable), and different network modules. But all switches in one stack must have the same version of IOS XE and the same feature set license. A mixed stack of LAN base switches with IP base or IP services is not supported. Catalyst 3850 Series Switches with a LAN base feature set can only stack with other Catalyst 3850 Series LAN base switches. The same applies to IP base and IP services as well.
https://www.cisco.com/c/en/us/products/collateral/switches/catalyst-3850-series-switches/white-paper-c11-734429.html
2.is it rule that in stack,we have switches in even number?
No, it can be odd or even numbers.
3.Can ws-c3850-12s-e take copper based SFP at its 12 port ?
Yes
4.when we buy ws-c3850-12s-e then do we get SFP with that 12 port or we have to order separately
Yes, SFPs need to be ordered separately.
HTH
