My anchor for the whole trip is the EuroVelo Network. Their website is not really great and it is most of the time quite opaque what the status of the different routes is. But it is a start. To plan everything in advance I find too daunting and there might be surprises along the way anyhow.
On a side note, I want to use this website to document a bit of the status of the different routes and provide a resource for people considering bike touring. This will develop over time. I will publish the gpx files for every single day, but only some days after, to not be too traceable.
Italy
I'll be starting in Italy, in Puglia. The original plan was to start in Sicily. But I found very little information on the bike paths there, plus: Sicily has a lot of mountains. I plan to make my start not too hard and basically very enjoyable. There's no use in exhausting myself so early in the trip and hating it. It's a marathon, not a sprint. I picked Southern Italy as a start mainly for the weather. I'll be starting end of February and the weather will be quite bad still in most of Europe, in Puglia it should be quite good for biking. Plus, it's not overly complicated to get there by train.
The starting point is Brindisi, marking the beginning of the EuroVelo 5 (which goes from Southern Italy all the way up to Canterbury and is as well called Via Romea Francigena). I will orientate myself on the EV5 to just South of Milan, where I'm going to switch to the EuroVelo 8 (the Mediterranean Route) all the way to Monaco.
I roughly plan a month for this first phase. I'll be starting slow and short, again not a sprint.