Lets talk about what type of wheelchair you need. If you read the actual rules you will see that most wheelchairs/scooters are permissible.
Obviously you can take a manual wheelchair. You can take a battery powered wheelchair. The only real requirement is that they have the non spill batteries.
My wife has this great Quantum battery powered wheelchair. I would never think of taking it since it weighs 250 lbs or more. There could be tight spots and you need a little flexibility.
For our travels we prefer the battery wheelchairs that can actually fold up if needed, weigh around 100-120 lbs. They are easier to handle.(see attached picture) If you purchase them they can cost anywhere between $1000 to $3000. Unless you are traveling a few times a year stay to the lower end since you’ll only be using is for a week or so. You can also rent them. This is especially true if your trip is your first. Once you have taken the trip, and have seen things you never thought you would, you will no doubt begin planning your next adventure. http://www.discovermymobility.com/store/powerwheelchairs/green-transporter/ez-ultra-lite/index.html?gclid=EAIaIQobChMIscHS6pXV2AIVz7jACh1_NgXDEAQYASABEgLP8PD_BwE
So now you have a wheelchair you are comfortable with. Can be manual or battery powered. Just up to you. If possible, get the wheelchair well ahead of time. Give yourself time to try it out, get used to it, make sure the seat is cushioned and you are comfortable in it for a few hours at a time. The seats usually come in several widths to before ordering it make sure it will be wide enough. They come with seat belts which will be important especially while touring. They come with battery chargers. The chargers will have US and Europe electrics. US is 115volts, Europe 220 volts. When you get to Europe make sure you switch the voltage or you might ruin the charger. We learned from experience. Also, these electric wheelchairs also can work as a manual wheelchair. You just make the switch in the back of the chair near the batteries and Voila, manual. They are light enough to use manually. If you, for some reason, intend to use it manually for the day you can even remove the batteries which will save about 40-50 lbs. Of course you need someone to push you since they don’t have the big wheels on strictly manual chairs.