Firstly they have reviewed their policy following problems on their Christmas cruise and it says "We have recently updated our policy on the responsible serving of alcohol and we reserve the right to confiscate alcohol at the gangway should the need arise. It is not our intention to invoke this policy as a matter of course and we will implement it only on occasions where we consider it is likely that the health, comfort, safety and enjoyment of passengers may otherwise be compromised.
Passengers under the age of 18 will not be served alcoholic beverages on board and must not be in possession of alcohol. Passengers may be asked to verify their age. Cruise cards for under 18 year olds will be marked accordingly. It is prohibited to attempt to purchase alcohol for those under 18 in the bars and shops on board. 16 and 17 year olds may be bought beer, cider or wine to drink with a meal in the restaurants when accompanied by an adult. Alcohol purchased ashore by those under 18 will be confiscated at the gangway." Given this is a wedding there maybe special arrangements you might have to ask the couple who are getting married what they have been advised. The voltage on the ship is 220 so no problems there. The luggage is what is allowed with which ever airline that si being used but normally max 23kgs per case. Can't help you any further maybe others will come in with further clarification.
Champagne is allowed on board and you can drink it in your cabin. If you want to drink it in any of the restaurants or bars you have to pay a corkage charge which I think is about £10 per bottle but it may be more by now. Hair dryers are provided but they are not very powerful so I would take your own. I have not flown to a cruise with Thomson but I have with First Choice in their premium seats which were wonderful - the food was good and there were lots of free drinks. The seat pitch, even in economy was good. May I suggest you register on the P&O site and join their Community section. You will find a section devoted to Ventura and you can get lots of answers there. Have a great time.
We flew home from our Ventura Transatlantic with Thomson/First choice (now one and the same) and we sat in the very back row and the leg room was excellent with tvs in the seat in front with plenty to watch and quizzes etc to do. Leather seats and very comfortable. My hairdryer in the cabin was fine quite powerful but I have short hair which doesn't take an awful lot to dry. Good food and drink and 23 kgs hold luggage with 5 kgs hand luggage.
I think you are asking is possible to take alcohol on board bought ashore.Well we did. I don't think P&O like it but the security people turned a blind eye.I will add however P&O did not allow the sale of bottles on the flight over there was of course the normal complimentary bar available.Air dryers are provided you will proably need a safety net to use it quite large[?] and resembles something out of star Wars.Luggage allowance 23kg pp.Seats leather Individual Tv Games etc extra charge for 1st run films decent leg room .One last point we did find Champange in the Carribean fairly expensive.I think the Champers on board cost about £30 for the house brand and about £40 for Moet.CONGRATULATIONS have a great time.