2,600km on an 8 speed bike?
The problem won't be the number of gears. Even 3 could be enough - if they were the right ones and you don't mind being slower. More important is the range, the difference between the lowest and the highest gear.

The range of the Alfine 8 speed hub is higher than what you would get of a traditional chain derailleur with only 8 gears (1 front, 8 rear). But its lower than the range of an Alfine 11 speed, a Rohloff hub or a common mtb setup.

I use an Alfine 8 speed on my commuter. I only really use gears 4 to 8. 4 or 5 are perfect to start from traffic lights, 8 is perfect on a slight descent.

The cog can be replaced to shift the gears in one direction (I plan to install a smaller one to get the used gears more to the middle, leaving the highest gear for faster descents or tail winds). That is not however something you can easily do on the road.

Whether the gear range fits your needs can be simulated with your other bike. There exist some gear ratio calculators online, most of them include the common internal gear hubs. Plug in the values of your Trance (wheel size, cassette sizes, ...) and find the ratios that correspond to the gears on the Bianchi (I think my Alfine came with a 20 teeth cog ... might be 22). Then try if those gears are right for what you expect on your trip.