Design a Buck Converter

That's a 1kW converter, which will be a challenge and require some careful engineering. You're planning a two-phase converter, so you're down to 500W per phase, and greatly reduced input and output ripple currents as well, good plan. I'm a big fan of Linear Technology's power controller ICs. For example, I used their LT3782 two-phase controller in a 300W 12V to 42V boost converter with very good results.

Linear Technology does make two-phase buck controllers, such as their LTC3729, which would be well suited for a 1kW converter, but it's limited to 36V maximum input.

So I think your solution is to use two higher-voltage buck converter ICs and synchronize them with your own external two-phase clock.

Take a look at LTC's LTC3810 100-volt buck controllers. These are current mode converters, which means two of them can be paralleled and will naturally share the output load. The LTC38110 provides a hefty 2A gate drive current, so you can use big MOSFETs.

One very nice feature, this controller can use the MOSFET's ON resistance to sense the current, and so does not need separate current-sense resistors, which would be painful at your high currents. But they do let you use sense resistors if you prefer.

"These are current mode converters, which means two of them can be paralleled and will naturally share the output load."

Actually, that's only half right. Both converters need to be running with the same control-loop current-setpoint voltage. That's on the I_TH node, pin 8, of these ICs.

Commonly smps controller ICs use transconductance (current output) amplifiers for this function, which allows the node's pins to be paralleled, but it looks like this part has a low-impedance 25MHz bandwidth op-amp output at this node. I think a call to LTC's engineering support would be in order, to ask their advice about the possibility of paralleling the outputs, or suggestions for other ICs.