General idea on Ipad

If you are buying a Wifi only iPad, it can be used anywhere. If you are buying your friend a cellular iPad, your friend should check with the cellular provider in their country to see what model is required. It may not be one sold in the US.

I would suggest you NOT purchased the iPad in the US and send to to someone in Europe. iPad warranty is NOT international. Should you friend have an issue with the device, it will need to be physically returned to you to take it to Apple for service. A better solution would be to send the money to your friend as a gift for them to purchase an iPad in their country.

One very important thing to keep in mind is if any repairs will be needed with this iPad, that your friend will need to either take it back or ship it to the U.S. to get it serviced. Apple's warranty is not universal internationally. You would be better off selecting the iPad that you would like to gift them, and then, send them the funds to purchase it themselves via the Apple brick-and-mortar store (in available) or the Apple online store using a credit card from that country.

Which specific iPad would really come down to what you believe they would use it for. Just about any iPad model will work for most general uses. The iPad Pro would not necessarily be required either, based on those uses.

Yes, the iPad should work in Europe just fine. No specific model required. They will need to get plug adapter to connect the iPad to the wall socket though.

Note that if you buy the Cellular model, Warranty will be restricted to the U.S. So the iPad would need to be returned to the U.S. for repair or replacement under warranty.