This is the final question posed by my correspondent:
"How can you be as efficient as possible when your base is still fairly undeveloped and your confidence is fragile?"
This is an excellent question, and hard for me to answer. I have been there, with an undeveloped scholarly base and less confidence, but right now I don't have those particular problems. Thinking back, I remember struggling with whether I could write the dissertation, just get it done. I was dealing with very complex ideas and trying to come up with a brilliantly original theoretical framework. The first chapter in particular was very difficult.
Let's break this question down into three parts.
The base. I'd recommend doing an inventory of your base. Just sit down and write down everything that is part of it. Any foreign language you know; the fact that your advisor is a good one; that your university library has the resources you need; that you are a good prose stylist and have good time management skills (Include any positives in your happiness base too.) Once you have inventoried your base you will see where the weaknesses are. Maybe you haven't read enough theory, or don't understand what you've read. Make a shorter list of things you need to work on. Ok. Now instead of a vague and uneasy sense that you don't know enough to write a dissertation, you have a realistic assessment of your assets and liabilities.
Confidence. "Be confident!" is useless advice. Real confidence develops through realistic experience with successful performance. The most successful students are not even the most over-confident ones, because they can have more trouble when the world doesn't agree with their self-assessments. Realistically, almost nobody fails to write a dissertation because of lack of intelligence or because of a lack of a scholarly base.
Once again, I think the key is to replace vague, existential, infinite worries with very specific lists of things you can already do fairly well and things that still give you some trouble.
Efficiency. Yikes. The dissertation is hard work and will be inefficient simply because it is the first project on that scale you have done. There will be "wasted" work, pages you write that will end up on the cutting room floor. I have documents on my computer from my current project with titles like "rejected bits from Lezama Lima chapter." Here I will only say that regular work is efficient work. In other words, inefficiency tends to be more of a function of not having regular working hours, as opposed to sitting down for two hours and working inefficiently. The latter scenario does happen, but you can just average in those days with the rest and it will all come out ok.