Say the bto cost 400k, do we get to choose the level and does the price increase the higher the level?

The choice of unit and level depends on your ballot queue number. If there are 200 units in the estate, and your queue number is 1, then you can choose any unit, any level.

Obviously if your queue number is 200, then be prepared to just take whatever is left. Unfortunately, this is really based on luck - there is no way to get ahead in the queue.

Don't lose heart if you have a high ballot queue number though! There will always be people who would forfeit their place in the queue if their preferred units are already selected. HDB allows you to see which units have already been selected before your appointment.