We are assuming You talk about presentation during opening ceremony (there is also small presentation during display evaluation).
1. Length of the presentation should be ~3min as mentioned in the information letter. It would be nice to have more time but we don’t want the ceremony to last too long.
2. Basically there are no compulsory parts but it makes sense to talk about your team (university), your bridge, maybe something about manufacturing process etc. This presentation is not strict at all you can structure it as you wish, make jokes etc.
3. Yes you can show ppt and hopefully video also (with audio).
4. Yes there is internet but it would be good idea to download your prezi presentation just in case.