The M2TW Citadel forum would get more replies, but as long as we're in the HRE section I can give some HRE specific advice for Merchants. What I would try to do is to get a northern port so you can produce a decent navy. With this force you can park your ships east of Arhus blocking the land bridge, preventing any merchants from entering Scandinavia while sending all yours up there for the amber, iron, and silver. This will be your training zone where you can level them up a bit. However if you see a merchant getting close that you would have a good chance of acquisitioning you could let him through and use it as a opportunity to skill up. Once you get a decent level you can send your merchant to higher value resources or just send him around looking for takeover targets. I usually have a lot of watchtowers up and can spot a vulnerable merchant when they're in range. Sadly I would say that the computer merchants are usually much higher in skill than yours but if you see one coming just move off the resource as they won't try takeovers if you're merchant is not trading anything.