First person plural or singular pronouns for thesis presentation

Use "we" when referring to something you did as a team, and use "I" when referring to something that you did by yourself. That is what these words are for.

Using "we" and "I" consistently in this way helps to make clear what your contributions were, and this is often exactly what the jury wants to find out during your presentation. If you choose to not go with the above option you should make it clear in some other way what you did and what others did.

Of course, if there is a clear preference in the culture where you are presenting it is best to follow that preference, but you would probably not be asking the question if that were the case.

That's a matter of opinion. If it's your official thesis defense presentation, you're representing your work, so it would be fine to use "I". But others may prefer to stick with the common "we".

There is no 'correct' answer here. You should do what you feel comfortable with.

There is no rule you have to pick one exclusively. I would not bat an eye at someone using "we" for the collaborative sections and "I" at their sections.

Especially for a thesis presentation, everyone knows you and who your group is.