Sorry that I did not get around to answer your questions any earlier! And thanks for the compliment on my English! I am indeed German but spent some time living in England, had a British boyfriend for some time and now have an American one. I use English quite a lot regularly and not only just on the DIS.
All Fast was a term that was used on the leaflet that we got at the end of the cruise. I understood it to mean the time when the ship was all tied up to the pier at the respective port.
We did not stay in the inside stateroom for two weeks. The one that we were moved to did have a window, but with an obstructed view. While this was a nice bonus, I did not at all feel uncomfortable in the inside stateroom and would not hesitate to book one for a longer cruise again. I think it has a lot to do with personal preference. On our last cruise we got a verandah because of a discount and in the end we did not really use it at all. I made the point a few times to go and sit there, but I really would have been equally happy sitting on deck 4. I even kind of missed being able to sit and people watch a little when I was on the balcony. So for me, I now know that paying any extra for a balcony is just not worth it. A porthole, yes that is a nice added, but not necessary, bonus.
Michael and I discussed solo cruising during the Panama Canal cruise quite a bit and we disagree on it. I think I would enjoy it a lot. Michael thinks for him it would make no sense. So, I think there is no right or wrong answer. You seem to do well travelling on your own, so I guess you would like it. One of the things I liked about cruising is that it is so easy to start chatting with fellow travelers. I never felt odd when I walked around the ship on my own and there were plenty of people doing stuff on their own. Forexample the morning show I often went to had mainly people visiting there on their own, just a few tables had more than one person.
Hope this helps! If you have any more questions, just ask ahead, I am happy to help!