Biking across Europe - Questions about the trains in Turkiye

I'm about to about to take the plunge for my first long distance tour and I have some questions.

I'm starting in France, biking down into Italy, and then taking a ferry over into Greece and biking to Turkiye, Istanbul in specific. My return flight is out of Athens, so if I’m delayed or late or just straight up exhausted when I get to Athens, I’ll just chill there til I fly home. But, my current plan is to push past Athens, go to Istanbul for two nights, and then take a ferry to Bandirma. From there I then bike down to Izmir / Ceceme and then ferry back to Athens.

I’ve done a lot of research, but I struggle to get solid answers to all of these:

1. I arrive in Paris, I’ll have my bike in a box. I’m staying in Belleville. My current plan is to take the RER to Gare du Nord, and build my bike there, load my bags and stuff up, and then bike to my hostel. Is this smart? Is building my bike in Gare du Nord asking for any kind of trouble? Biking out to CDG airport seems like an absolute nightmare, and taking a cab seems super expensive.

2. On the subject of nightmares, biking into Istanbul seems super bad, so I was thinking of taking the commuter train in from Corlu to skip all the highways. Is biking directly into Istanbul as bad as I think, and is taking the commuter train smart? I've read that bikes can be difficult to take onto the trains, but I think that's for the bigger ones? I've also been thinking about taking a train from Thessaloniki to Alexandoupoli because I've heard that stretch is pretty brutal with little biking infrastructure.

3. After Istanbul I'm going to ferry over to Bandirma, I was going to angle myself and cut through the middle, hoping to get to the coast near Ayvalik, and then reconnect with Eurovelo 8 into Izmir / Ceceme. But what’s the middle part like? Is it bikable? Is there stuff? It doesn’t seem like there’s a lot of bike infrastructure, but it also doesn't look like megahighways. Or is it smarter to hug the coast the whole way down?

4. • it's a big trip, so any tips you have about my route are super appreciated