Ok, so this is going to be really long, so please bear with me. Also, if i posted this in the wrong section, I do apologize.
My fiance and I are going to be heading to Europe from April 27th to May 6th. It is her second time outside the country in her life (last year we went to the bahamas, not exactly a long flight from the east coast of Florida) and now this trip. I have been to Europe a few times, but when I was much younger (about 10 years ago, when I was 15).
We are taking Virgin Atlantic from MCO-LGW in PE (seat 79 A&C if anyone has any experience in those seats, please let me know, im worried about the recline as its the first row in front of the stairs).
She wants to see London, Paris, Venice, perhaps northern England and possibly Wales. She knows there is not really enough time for this so here is what we had planned.
April 27th- Land in London at 815 AM.
Travel to the hotel, spend 2 days in London
Morning on the 29th, take the Eurostar to Paris
Depart paris the night of the 30th for Venice
leave on the morning of the 2nd of May to go up to Wales or northern England.
Spend some time there, come back to London on the morning or afternoon of the 5th and then depart the morning of the 6th back to MCO

counting the days until we return again.
So here are the questions:
1-Assuming all travel except the eurostar (which was a lot of fun when I took it last time) is done by air, does this seem reasonable to get a good taste of a lot of different culture and sites? (I know we wont see nearly everything)
2- is it better to arrange a guided tour of the places we dont speak the language such as Paris? I've heard a good guide can really enhance the experience and you don't have to wait on the lines for the tower, but they only go to the second level, and I would very much want to go back to the top. If we use a tour, who should we use? I've seen some "sketchy" sites that seem like ripoffs............if its too good to be true, etc. etc.
3-where should we stay in Paris and Venice to really get a good view of the city
4-Probably most importantly. Where is the best place to go to see some castles, my fiance has not stopped talking about going to see them and is very excited, where can I find the best ones to take her too?
5- Is it worth it to spend a day at versailles or should that wait for the next trip when we can devote more time to it? I was there briefly and it was absolutely beautiful ^
6-any other tips or hints would be greatly appreciated, we are both growing more and more excited by the day and even though I have been there before, going with her is going to make it like it is the first time, so I can't wait
Thank you for all the feedback.
P.S. The only thing we have booked so far is the Airfare, she wanted to keep it flexible for now, and she purchased about 15 travel books to look for things to do and set a tentative schedule, but she wants to keep it "loose" so the schedule is totally changable