Question

Would be nice to set the loop markers to fit the range of a specific arranger part (in the rightclick arranger part context menu or key command).

Answer 1

I hope I got your question right, maybe this will help you.

There is a very helpful bit hidden option for this. If you right click on the loop symbol in the transporter section, there is an option for "Loop Follows Selection". If you tick it on, it will loop your arranger track selection automatically.