Try some long holidays with a camper before you even consider buying one.
Life in a camper is different from what you imagine. You both might like it but you might hate it as well. Both people have to accommodate to a lot of things and need to have a good relationship, because there is no place to hide when things get rough.
The bigger the camper the less mobility you have (think of managing in urban traffic and small roads) and the more power the engine needs to bring you up hill. Also the higher the fuel bill will be.
The one camper that can be ideal for touring Europe will be a flop in a country with dirt roads full of holes and sand dust. There you will need something mighty in my opinion. A camper for cold climates weights more and is more expensive while in mild weather countries a light model with less space will do, as you can just have your living room outside and sleep with windows open.
The nicest campers I ever saw were build on a chassis of a (Mercedes , Volvo and Daf) truck or on a land rover and were one of a kind.
In poor countries they manage to repair almost everything while in rich countries they will send you to the dealer for spare parts and expensive reparations. So don't buy anything falling apart that will let you down half way and cost lots of money and irritation.
Going around the world with the same camper seems a lot of extra work and a waste of money to me. In the USA you can buy a second hand and travel the continent with it. The same goes for Australia and N Z. But first try some months at home. One month isn't enough. You need to learn to live and enjoy life in such a small space in different seasons. I know from experience it can be quite nice when the weather is ok