Slow cooking in stainless steel pan

Hi!

So I brought myself a few stainless steel pans today. I realise they should be heated first, then fat added etc
However what if I want to make a slow cooking sauce. For instance, spaghetti with sardines. Usually I'd slowly brown onions in the pan,
Let them caramelise, then add sardines oil and then cooked pasta. From what I have seen online, this will lead to sticking? Any way around this problem?
And what about shrimps? I normally cook them slow on a low light. Do shrimps cook well on a high heated stainless steel? Or is anything ok so long as you stir it frequently?
Thanks!