..GO TO THE "CONTROL MODE OF AN SMPS" folder of the above free smps course.
It will show you what is VM and CM in the ltspice sims.
But basically, even with VM, you need current sense in the fet source...for safety reasons.....so you may as well use that source sense for current mode control.
Read up on Dr Ray Ridley...he did his thesis on current mode control and can tell you why current mode is generally better than VM.
Eg with CCM buck, the dynamics are more complex in VM than CM.
In CM, you cancel out one of the poles of the double pole response of the buck inductor and cap...so its easier for you to get stability.
Read the pcb layout doc in the above course, to answer your concerns on that..i also attache here.
An opto for high side drive is not possible unless your f(sw) is ridiculously low. Optos are too slow.
Use either...
Pulse transformer.
High side supply & digital isolator into fet driver......or
Bootstrap high side drive.