Hi,
StackWise Virtual Link (SVL) connections are established only through 10G or 40G up-link ports on the supervisor module. You cannot establish an SVL using a 10G port on one switch and a 40G port on the other switch.
So, yes if you want to build a Stackwise virtual environment, you have to use the ports from the sup for the VSL.
If you use say 2 10Gig ports for VSL, you can use the other ports for down-link or up-link.
See link for more info:
https://www.cisco.com/c/en/us/td/docs/switches/lan/catalyst9400/software/release/16-9/configuration_guide/ha/b_169_ha_9400_cg/configuring_cisco_stackwise_virtual.html
If we can perform all of above features, is that mean I no longer need 10G line card anymore?
If you only need 8 10Gig ports total including the VSL links, than you don't need any 10Gig module but if you need more than 8 than you need to install a 10Gig module.
HTH
