Advice on milling mild steel with cnc mill

So it will be the first time I am going to mill steel on my CNC mill. Firstly, The mill is 1980's. It weighs 1.1 Ton / Max Spindle Rpm 2500 / 2.2kw motor. I am using Fusion 360.

I have a 20mm thick piece of mild steel. I want to face it down to 12mm. I have a 5 flute 50mm Shell mill with carbide inserts. I have used it on aluminium with different inserts for ali with good results. Online calculators don't seem to give me a very good starting point for this shell mill.

What doc could I take without pushing the tool to hard ?. Speeds and feeds would be helpful to the relative doc