how to Stack two Fortiswitches without fortilink mode

[midel1989]

HI guys , i not familiar  with fortinet device as well , my company bought some fortigate device and wants me to design the network 

one Fortigate 100E maybe two in future  , two fortinet switch 248 E POE and two Fortinet 224 E POE , i want to use 2 tier network ( collapse Core) for design , i want use inter vlan routing in core switch not fortigate , my thought was use 2 forti 224 e as a access layer , 2 fortiswitch  248E as a core switch and connect them to fortigate also i want connect all nic servers to two core switch ( aggregate two nic from server to two port one from each core switch ) , could you help me out how can i design my network?

please be aware i don`t want all internal traffic goes to fortigate i want core switch manage intervlan routing and also stack all switches together 

I am really appreciated