Hello,
so I started the humble merchant line, followed part of a guide so now I'm going around on an Iguana Vanguard doing various missions, and I just bought a Mercury super freighter for 130k. Don't know if it is a good deal but nevermind.
I upgraded it with engine and rudder, put a pair of shields and installed the Trading Software MK3, before sending it in Ore Belt for doing hopefully something.
Now, I understood reading around that this particular piece of equipment gains levels, and therefore extended trading possibilities, from sector to universe. How can I monitor this levelling, so that I can know when to change the auto trade scale?

After starting a sector trader, wait until they reach their starting sector and then you can check their level by reading the description at the top of the ship's command screen. It'll contains the pilot's name and their level in parentheses.