Hi honey, I'm sorry that we haven't got to you as quickly as you would have liked, it's Saturday morning here so not altogether an easy time to put a good, well thought-through response together.
I don't want to leave you hanging though so I shall do my best. First of all, hugs
I am sorry you are finding this so hard, the difficulty is that there aren't really answers to your questions. We will not be able to say yes he will sleep for 11.5 or 12 hours after a particular BT and he may not do anything immediately. If you feel the best thing for you as a family is to go for a mix of NNDs and occasional naps days to help Benji catch up there will need to be an element of going with the flow, as we won't be able to help answer what time to nap or sleep every day. So if you don't feel able to manage going with the flow then cold turkey to no naps at all will provide you with the consistency you look for and this consistency will be God for Benji in the longer term too.
During this time there are going to be some early WUs nd long long days, my suggested plan would be:
1 set BT at a time you can feasibly manage every day, and stick with it no matter what;
2 use a gro clock or lights on a time and set that for the same time every day, if Benji wakes before the sun comes up, it is to be treated as a NW and so he stays in his room and you reassure him if he needs it;
3 if he is super super tired he may need a little catch up nap at some point but this will need to be something you go with the flow a bit on, a little cat nap type thing when he's clearly not going to make BT if you see what I mean.
As for activities, you can do your usual activities but he may need some quiet days to cope during the transition, you'll have to try it and see how he manages really.
I'm sure others will be along later with more detail if you need, but for now honey if you feel that going with the flow is too much, and you feel that naps arenMt working then this does seem like the best way.