Great Tit nesting habits

We have a nesting box in our garden and a Great Tit has built a nest. It has a camera, so we have quite a bit of information.

It starting building the nest on Tues 19th March. It took about 5 days to complete. It is now lined with soft material.

The Great Tit started to roost in the box every night from Tues 26th March, so that is just over 2 weeks ago. It hasn't missed a night. The Great Tit leaves early in the morning and returns at dusk.

Q1: A basic question. Do Great Tits mate and then build the nest, or do they build the nest then mate?

Q2. I gather that the female builds the nest and the male is largely absent at this stage. Is that correct?

Q3. Do you think it likely that she is laying eggs at this stage?

Many thanks,

Craig

UK, North West