Thoughts/Advice on My Way France Tour/ visiting Spain

If your time in Spain would be short, I'd recommend either Barcelona or Madrid. Both have lots to see (though non-art-lovers will probably need to take more advantage of the great side-trips possible from Madrid). You could cram both cities into a week (especially if you don't care about Madrid's art museums), but you'd miss some wonderful sights.

How many nights would you have in Spain, and what time of year do you plan to make the trip?

I'm not sure what kind of advice you're looking for, but here are some things that come to mind:

If you see both Madrid and Barcelona in a week, you will get a taste of each, and I think that's fine for a first visit. However, you should look at what there is to see and do in each one, because as acraven says, you may find a few days insufficient, and will want to spend most or all of your time in one, including daytrips to area attractions (such as Toledo for Madrid, or Montserrat for Barcelona).

To get between Madrid and Barcelona, by far the easiest way is the high speed train. This is much cheaper booked in advance. To do this, you will need this tutorial from TripAdvisor: https://www.tripadvisor.com/Travel-g187514-c80518/Madrid:Spain:Buying.Renfe.Tickets.Online.html. You should also use PayPal from the outset, as the Renfe website usually doesn't work well with US credit cards.

I see the My Way France tour ends in Nice. Before booking any flights, investigate flights from Nice to Madrid and Barcelona, as well as flights from Madrid and from Barcelona back to your home city, so you can see if there is a financial advantage to starting in one or the other. To find flights within Europe, use Skyscanner: https://www.skyscanner.com/

If you were thinking of taking the train between Nice and Barcelona, a quick look on the Bahn website shows that it's over 8 hours for a "quick" connection, and some take much longer. To find train schedules and prices for this route, you can use Trainline https://www.trainline.eu/search/nice/barcelona/2018-02-15-08:00, since it will sell you the whole thing in one transaction.

The time of year could be critical. If it is summer, Spain can be very hot.

Good point about the weather. In the summer, Madrid and points south tend to be hotter than Barcelona, but it can get up into the uncomfortable range in Barcelona, too.

I think you want to go France because the surrounding area is too good so may I request please the France area.

I did the "My Way France" tour as a solo traveler in 2016. Spent a few days in Paris prior to the tour to visit Chartres and Saint Denis, as well as the lovely sights of Paris. Also spent a few extra days in Nice at the end of the tour. Nasty business about the truck attack just after we were enjoying the Bastille Day celebrations at the beach. No matter; it's the world we live in. Much appreciated the excellent coordination of the logistics, etc. and the ability to either do things on my own or with my tour mates and can highly recommend! Barcelona & Madrid both as add-ons for just a week, not so much. Both are easy to do but, either city would be a week well-spent. Loved Madrid but Barcelona has so much to offer in a very different way. Of the two, Barcelona was my favorite. Happy travels!

Frank's observation was my first thought reading the question. Visiting Spain depends so much on the time of year and your tolerance for heat.