Automotive Power Supply Design. How to start

I am trying to design a DC-DC supply that should work in Automotives (Cars - 12V Batteries Only)

The requirement is

Output:
1. 7.5 to 8V about 12 amps
2. 5V/1amp
3. 3.3V/1amp

I havent worked much on automotive power supplies as yet.

I have gone through a few details but I get information where we can generate 5V or 3.3V at lower currents.

I understand that there are a lot of things to consider with Automotives, be it voltage variation on cold crank, load dump, EMI issues but I am not sure how and where to start

I have designed a few DC-DC but not automotive.

An automotive supply is just another supply, but designed to withstand the electrical events of an automobile environment, such as reversed battery, load dump, cold crank, and such like.
It must work also across a very wide temperature range, from -40 to 75C, if I remember correctly.

There is a very comprehensive SAE spec detailing the requirements. I'm sure there is an equivalent IEC spec.

O/k, +12v battery input only, and the output needs to be +8v max.

So it looks like a purely step down requirement. A healthy battery should not drop below 8v during cranking. If it does, the solution is a new battery, not a better dc/dc supply. The main thing during engine cranking is starting the engine, and as long as the ignition still works, it usually does not matter if other things do not.

Its also quite possible that in a vehicle, an isolated supply may not be a requirement, so a simple buck regulator may be all that is needed for the main +8v output.

The two lower voltage outputs can best be served with linear regulators, working off the main +8v output, as the power requirement is fairly low, and efficiency will still be pretty good.

It will need some high voltage transient protection at the input, and be safe for load dump input voltages, but a buck regulator should be able to handle that with ease.

Many of the control chip suppliers provide sample circuits that produce high current outputs at +5v.
A slight tweak should see that increased to +8v without a serious redesign.