You need reasons to try and control somewhere, especially somewhere as far away as Alaska is. What do they get out of Alaska that they wouldn't get out of Sakhalin?
Seems really implausible. The communication and supply lines going through the Med are pretty likely to be cut off by the Spanish at some point. Going through the Red Sea is an absurdly long distance, even Australia is probably too far for that for most of the colonial period.
A temporary and...
Yeah, even if it succeeds in Germany, you need to prevent UK/France intervening. Maybe if the war limps into 1919/1920 and then ends, the UK and France might be too riven with internal unrest to make invading Germany palatable?
Except that Overlord waited until the Luftwaffe was barely a factor to oppose the landings. Where would they have hidden 2000 planes, and housed the pilots?
Could an Austro-Hungary-like disintegration occur before the Ottomans join the war (and thusly don't join the war), but late enough that Britain and France are too distracted to intervene?