1. Your assumptions don't much matter. You were given a Costs Agreement
(and almost certainly an accompanying Costs Disclosure) when you started.
And, you had (have) an ongoing right to be briefed on costs as you go.
That you chose not to exercise that right is not the question.
2. I bill like
@Rob Legat - SBPL - some stuff is a fixed fee for "all work", other things are billed per hour.
Different billing structures for different kinds of work.
Not that I speak for other lawyers, but this is how a lot of us do it.
3. Even though I personally disclose them, I have found that some line items
don't make sense to lay people.
Time spent in reserach and, in particular, "consideration", for example.
The latter can mean, literally, thinking about the problem and working out what to do.
That is, the application of
our knowledge and skills to
your problem.
4. They could in theory chase you for the outstanding amount.
However I suspect that the outstanding amount is exactly the same number as
the opportnity cost of doing so, compared to getting you off their client list.