0) Less is more. The landing beach is a bottleneck for logistics, so the worse the infrastructure available to your enemy, the better.(A)
1) poorly defended major ports to capture intact would be a bonus, but high/defensible ground close to the landing area can work in your favour if you reach it and reinforce it before the enemy can. Here the poor infrastructure can be overcome by light forces and air drops. There are few good invasion beaches, true. Lack of bristling defences is hard to find unless strategic surprise is complete.(B)
2) While the rail line does offer good logistic support, it is easily negated and hard to re-route if repairing. All the same, I don't think anywhere is ideal to make landfall on the continent with such an unpleasant reception awaiting them.(C)
3) Which is why I really like the idea of further island gains to put pressure over an extended range of coastline. The same holds true for islands leading north into the Aegean. Perhaps other islands (Norwegian around
Smøla say) too?
wiki/List_of_islands_of_Norway_by_area
Bømlo was actively involved in the
Shetland bus operation. Could an invasion sneak in piecemeal?(D)
A) Against the Italian Army alone, I am more than confident that the British Army can chew their asses out royal. A war of attrition outside the landing zones that the Italians will have no stomach for. When did the Italians EVER kick British ass without the help of the German Army? There is no making up for lack of first-grade equipment, training, and leadership. Numbers alone simply won't do it.
I see the Italian Army in Sicily representing the greatest of logistical impediments for the British Army in terms of handling all those POWs, and that's about it. Mind, until Syracuse is secured, repaired, and made fully operational, that impediment will be very serious. At least the British will have the partisans to help (Mafia). The US Army can take the lead on that score.
B) If there was one thing about Hitler's interference in military affairs in the West that was actually very successful, it was his obsession over hardening the ports.
I wouldn't worry too much about needing defensible terrain immediately outside the landing areas. Defensive battleship and cruiser gunfire support had a tendency to do grand scale urban renewal on any panzers foolish enough to try "driving the enemy into the sea". Frex, what happened to the Herman Goering Panzers in Sicily, the German counterattacks at Salerno and later at Anzio, the 21st Panzer on D-Day against the British (?) landing beaches, and the German Seventh Army at Avranches.
C) Not sure of your meaning here? That rail line running down north to south through Yugoslavia into Greece is in pretty rough terrain. The Germans proved that they were lightening quick at repairing rail link breaks, except when done by massed heavy bombers in daylight. Those breaks could take weeks or months to fix.
Ironically, the best two places for landing zones are as OTL. The sites of Overlord and Dragoon. They knew what they were doing. Southern France does have a few downsides unfortunately. You can't exploit into Italy through the French-Italian Alps, it represents the long way through France to Germany, and the terrain in Southern France is the worst in the country, much of it either mountainous (along Switzerland and Spain), broken, or rough. But defensively, if the Germans decide to do their all, it is also the easiest to hold.
D) Norway? No. Just NO. Just put it out of your mind. Even if the Japanese were to surrender in the next update, and the whole of the heavy units of the Royal Navy, US Pacific Fleet, and US Marine Corps were sent to the North Sea, they couldn't make Norway work as anything but an elaborate, and very costly diversion.
Logistically totally impossible. The ports along the North Sea simply cannot support an invasion to liberate such a rough and mountainous country. Especially considering the garrison strength in country. Norway, like the Channel Islands, made for a very good self-sustaining POW camp. We didn't even have to feed them. Granted, they were still able to interdict the Murmansk Convoys and use the port of Narvik for Swedish iron ore, but it wasn't worth going after Norway for that.
Why is all this true? He who rules Oslo and Copenhagen rules both Denmark and Norway. Those two major ports, along with the Norwegian rail network (leading up to Trondheim) allow easy support and reinforcement of the heavily overloaded (too many troops considering the remote nature of an Allied threat to liberate Norway) captive country of Norway.