one guy said to yellow colour cores are for filter and such, so to avoid. Black ones are ferrite and are suitable for induction heater.

Think you will find there is no set color codes for toroidal cores, like there is for resistors. Why not just buy the correct inductors? They will be wound smoother and work as designed, and not just a guess. https://www.surplussales.com/Inductors/Index.html That same company sell the box caps https://www.surplussales.com/Capacitors/Polypropylene/Index.html And they ship world wide.

 

I'm dropping the royer oscillator circuit and moving on to half bridge driver to drive the coil. I don't have beefy linear power supply which is required for royer oscillator to work.
I have designed (TBH, copied bits from here n there) a circuit which consists of a oscillator and driver. Control ic is TL494
Will this circuit work? If yes, then i have other questions too.
If No, then what changes needs to be done?

 

The automatic phase and frequency adapting (PLL) circuit (CD4046). Without of that any use of forced resonant contour driving is faulty.

 

I'm dropping the royer oscillator circuit and moving on to half bridge driver to drive the coil. I don't have beefy linear power supply which is required for royer oscillator to work.

Why do you think that that will work with you SMPS? SMPS aren't made to drive current hungry things, they aren't even recommended to power DC motors or stepper motors. They lack the "headroom" when power is needed they just won't keep up with the power draw. That is the reason to use a linear power supply.

You said you don't have a linear supply. Do you have all of the transformers for the half bridge type?

Look at this link and read all of what he has to say. https://www.spaco.org/Blacksmithing/ZVSInductionHeater/1000WattZVSInductionHeaterNotes.htm

 

Actually not, smps are rated for 30apms and without anything inside the workcoil it should not consume whole 30amps and even more the voltage drops down to 1.7V
Something isn't right here.

You've managed to create a short circuit.