we would like to upgrade our Magento 126.96.36.199 installation to 1.8 with around 40000 products and 25 store views.
In the past, we had bad experience upgrading our system. Our first installation was Magento version 0.8.
So we would like to test the upgrade risks before.
What is the best way for upgrading?
Making a new Magento 1.8 installation, and then connect them to the old 1.7 database?
Or set up a developer system and start upgrade process? How to set up a developer system for 25 store views?
Setting up and testing the new system might take a while. During this time, we might get orders in the old Magento installation. How can we get this orders sync with the new system?