Honestly, I'd recommend that you search CL for the bike you want rather than convert what you have. Those simple conversion projects often end up being not so simple and costing more than in the end than what the bike is worth. With single speeds having a high hipness factor right now, you may even be able to find a used 5 speed for less than what your Bianchi would fetch and make money on the deal.

If you really want to stick with the Bianchi, then your parts list is pretty close. But most likely you will need a new back wheel. If your current hub is a flip flop track style hub, you can't just add a 5 speed cassette to it. You'll either need to find a used wheel, or buy the hub/cassette and have someone rebuild your wheel using the old rim. But by the time you rebuild your wheel you're starting to get into some real money which is why my first recommendation is to find a new (used, but new to you) bike that has the features you want.

It takes longer to change the tube on an IGH bike, and it likely requires more tools. That's pretty much all there is to it. I'm assuming that people can make their own decisions about whether or not an IGH bike is practical for their needs.

https://www.rideoncables.com/en_us/

The inner wires are coated with PTFE, they travel inside a very tight conduit/liner which is separate from the also lined housing, and a "grub seal" innovatively keeps all weather out from the derailleur end of the cable. Somebody (not me) once accurately stated, "You only change the cables when you change frames".

They are truly remarkable for shifting, just so much faster and more precise than any other cable system with the added benefit that you never need to adjust them unless you remove a derailleur for major overhaul. I swear that my 1994 MTB that goes through hell and high water (literally) every winter shifts faster and more precisely than my $7000 road bike which doesn't have these cables (yet).