The Curse of Tippecanoe continues with worse 9/11

Honestly, I don't know. I'm not so mindful of, or expert in, the details of 9/11 events to give you a definitive answer, and at first glance several factors may be involved, such as the point of origin of the planes, the time sequence of the hijackings, their routes, and so on. So I'm going to answer "butteflies align to yield whatever seems to work best for the narrative purposes of the scenario".

It seems an entirely feasible and reasonable event sequence to me, except you got the POTUS and VPOTUS wrong. In this scenario, the President dies in the attack to the White House, the VP survives and succeeds him. For simplicity I tend to assume him or her - a female VP is hardly unreasonable in 2001 with the right political butterflies, as someone else pointed out - survives because they are on travel on the date of the attack.

Yep. Optimally a NATO base close enough but somewhat distant from any major European city, if the Euro branch of the terrorist attack wave already started as well. Death of the Speaker of the House and President pro tempore of the Senate isn't so important for continuity of the government in this circumstance, since the VP outranks them in the presidential line of succession, and if you ask my opinion, I agree with several scholars that they don't really belong there at all, their addition in the 1947 law was a mistake for various reasons. ITTL the mistake gets corrected in the aftermath of the attack and the law is reversed to the 1886 version, with the Cabinet members coming after the VP, with the ATL addition of Homeland Security, state governors, and the list running in order of Department and state importance.

Yep. As a matter of fact, when I originally conceived the scenario, I thought of the terrorists using something more like like ISIS tactics for the Euro branch of the attack wave, instead of hijacked planes as in North America, but it might well happen the other way. It doesn't matter much, apart perhaps from puzzling which European targets the terrorists might pick in the latter version. What makes a real difference is the US leadership getting partially decapitated, and Britain, France, Germany, Italy, Spain suffering a damage of their own that is the combined equivalent of the American one. Well apart from the political butterflies arising from the 1981 PoD, and the Middle Eastern ones giving getting ISIS-style territorial control to Al-Quaeda.