When to take questions during a thesis defense?
The following is written from my perspective and it reflects my biases. 

If someone feels the need to ask a question during your presentation, chances are it is because you failed to explain something properly and they don't want to get lost. I, for one, hate it when a speaker just barrels through difficult material and I have to struggle to keep up (one time, the speaker pulled up a slide full of long lines of lambda calculi and went "as we can clearly see here..."; avoid that). Go through your talk plan carefully, identify the tricky issues, and make sure that you don't have hidden assumptions lurking anywhere. If in doubt, assume that the audience won't be able to follow you unless you explain things carefully. This much should ensure that all the questions come at the end and, more importantly, that they are substantial (i.e., none of this "I didn't quite catch your definition of blah, can you repeat it please?").

As for thanking your advisors, it's appropriate if you keep it short (like 20-seconds-tops short). You already have the acknowledgements of your dissertation to wax poetic all you want.