if the british fleet is somewhere else and you concentrate your whole fleet you should be able to get upper hand in the one region. Also assagain a lot of bombers and figther to that region and than land and support it with a handful of paratroopers around important ports. So should be doable.
you only need sea lane superiority temporarily, in lanes that are in easy range for german planes to assist (NAV especially) to launch across the first division, at which point the rest can just be ferried over to the captured port.
it shouldn't be too difficult to achieve unless the UK wants to spend a disproportionate amount of time and energy trying to stop you from ever achieving naval supremacy there, at which point the italians take malta and gibraltar because the UK was messing around
Also, those planes can be (and historically were) supplied from Denmark (Jutland is literally just about 100 km from southern Norway), so a good idea would be to fully conquer Jutland before you try to take Oslo and Copenhagen. Historically, Denmark was in general used as a means for transportation, as suggested by General Nikolaus von Falkenhorst.
Now as you say, the British could probably still deny access to Norway by focusing their naval forces in Skagerrak, thus further justifying going for complete control over Jutland if you ever want to take Norway, regardless if they have fortified the area or not. Edit: Personally, I wouldn't bother with Norway. As long as I have control over Denmark and decent relations with Sweden, I would assume they start shipping their ore through trains down to Malmö or Karlskrona if I ever need to trade with them. I would have total naval supremacy in Öresund and the Baltic Sea considering I control the Danish straits and the Kiel canal.
The threat of British naval intervention was also the very reason why the original plans for Unternehmen Weserübung were kept so top secret that not even the commander-in-chief of the Luftwaffe, Hermann Göring, was told about them until just a month before at a meeting with the meeting at the Reich Chancellery with Hitler, the other two commanders-in-chief, and von Falkenhorst (Source in English: German Northern Theater of Operations 1940-1945). In order to utilize the element of surprise, the Danish foreign minister Peter Munch was told only after the operation was already underway by the German ambassador in Denmark, Cecil von Renthe-Fink, that there were German troops on their way. In order to justify this act, he also told the Danish foreign minister that these troops were there to protect Denmark against a potential French or British attack, and demanded that all defense was to be ceased. (Source in Danish:
http://milhist.dk/slaget/den-tyske-besaettelse-af-danmark/)