We make sauerkraut every year.  Or, rather, I do if I can't bum some from my sister who makes it by the 30-gal crock… 

If no scum's forming, don't worry.  If the temp's cool enough where you store it and all the cabbage is below the brine, it might not form.  It's mainly just airborne yeasts and sometimes molds.  If the brine's salty enough and nothing sticks above the waterline, then it's hard for them to find a place to perch, kwim?

Do you like your sauerkraut with a little bit of crunch?  If so, you'll want to stop the fermentation (and can it, if that's how you plan to store it) before it gets soft, loses the crunch.  The only way you can really tell if it's ready is to taste it.  Some don't like this part because it may be hard to get past the scummy surface to accepting that there's something you want to eat hidden in the brine. :D

I know the 3-6 weeks range seems rather large but it all depends on how you like your kraut.  I just went to a Sandor Katz fermentation workshop put on by a new food co-op near here and he had a story about giving out samples of what he thought was a pretty well-aged kraut, still with a bit of crunch but tangy.  Someone tasted it and commented that it was okay for cole slaw…  Then, when he'd run out of the "good stuff" he was giving away samples of kraut that was pretty "fresh", only a few days old.  According to Katz, quite a few people loved that kraut — said they'd never liked sauerkraut before but this, this stuff was good!  All depends on what you like…

No experience here in adding sugar to sauerkraut but other than making it sweet, which seems to be something you think you might like?, can't see there'd be any harm in it.  You can always rinse the kraut before eating to help reduce the saltiness.

Note:  I don't want to fret.  So far it all sounds great.  And I use stainless steel pans for acidic stuff, too — where the directions indicate non-reactive containers (glass, plastic, porcelain, wear-free enamelware, etc.)  But carefully check over your pasta insert before you use it again as most stainless steel cookware is not stainless steel through and through.  Often there's a core metal used with SS plating overtop.  Sometimes, particularly in colanders and other dishes with holes, the stainless steel outer layer can wear thin and expose the other metal(s) which are usually reactive.  (Ask me how I know…) Those large (gallon, half-gal) pickle jars can make a good sub for a crock.  Make a cardboard sleeve to fit over them if contents need to be kept dark…

Suzanne,  We have crocks, but they are difficult to deal with.  Hard to get into the sink to clean, heavy and slippery if you want to move them etc.  For years now we have used food grade buckets  for fermenting.  You can usually buy them from restaurants or deli's for a dollar or so.  I like the ones that had pickles in them if possible,  frosting buckets have a nasty sweet smell that is difficult to remove.  The main reason we prefer the buckets is that a glass pie plate will fit down inside, with  doubled plastic gallon bags on top of the plate ( partially filled with brine in case of leaks) and the bucket lid resting on top you are good to go.  Having a handle they are easy to move,  do keep a tray underneath just in case.  This works for us maybe someone else can use the idea.