Palenque

Ditto to what annhig says - for years i just hopped off the train and looked for a hotel - often first going to the Hotel Booking desk in most main stations - or Tourist Office which booked - or with a guidebook just went around

and yes it is time-consuming and more expensive as the cheaper ones book up first

So now i do everything online before i go - securing the best deals - places that could well be full when i arrive

Thus i do put my itinerary in stone but at least when that train rolls in i'm off and often at my accommodation within 30 mins - you could wait longer than that in the line at Rome Termini's hotel booking desk

HuisClos

I think your itinerary is great, but I agree that since you're coming all the way from Vancouver (and will be jetlagged), an extra day in London would be good to acclimate yourself. Plus, there's so much to see and do in London, especially at your age.

Since you are an art "neophyte", maybe best (if you need to delete a day from one city to make the extra day in London) to either take it away from Florence or from Barcelona.

Based on what you said about Paris (and I'm guessing that most everyone is in agreement on what you said about Paris!) that you should not take one second away from Paris.

I don't know if you've been in a non-English speaking country before, but if you have not, and haven't learned French in BC, you might give some thought about going from London to Amsterdam to Paris to kind of get immersed slowly into the language differences, because you'd have more luck finding someone in Amsterdam who speaks English than you would in Paris -- only based on my own personal experience, and may not be fact!

Since you're going to be doing a lot of traveling, I'd suggest booking rooms beforehand and not waiting until after you get there -- that way you'll know exactly where you're going when you get off a train or plane and won't have to sit around in some terminal trying to: (1) pick a place; then (2) find it.