You want the best full detergent 15W-40 diesel oil you can get.

You want to run the engine in the 2000-2500 rpm range for 20-30 minutes to break in the cam, go to any cam makers website or I'll give you links if you want. You need higher than 1500 because the B20 does not have a big oil gallery running along the side of the lifters like they do in American 6's & V8's. The reason for running at 2000-2500 is to reduce the pressure of the springs on the lobes & to ensure that there is plenty of oil flinging around in the crankcase.

I'd drop the oil out after the cam break in period & check for anything shiny. Then make sure all the lobes survived. You absolutely do not want to be driving around for 500 miles if the oil contains the ground up remains of one lobe mixed in it. That does your rings & bearings no good at all.

I'd only use 2 litres to prime & tip the other 2 litres in just before you start it so that you have a bit around the lifters.

then ~sinusoidally 1k~3k for 30 minutes to seat the rings, valves, etc

Actually, the rings don't do any bedding in while doing the cam break in, you may even notice that the blowby increases during the first 20 minutes. The rings will bed in when you get on the road & give it full throttle around 2500-4000.