Bosphorus express, is it worth booking with interrail?

Hello I am planning to Travel from Bologna to Istanbul.
I will arrive in “Bucuresti Nord” at 15:05 and plan to take the Bosphorus Express on the day after at 10:50.

I read in this forum that I have to buy tickets for the latter in the Bucuresti station (I should have plenty of time)

What I don’t understand is how the reservation works.
On the interrail website it says that a single cabin sleeper is € 77 on top of the interrail pass
https://www.interrail.eu/en/plan-your-trip/tips-and-tricks/trains-europe/night-trains/bosphorus-express-night-train

But on the Seat61 website I can see that the price for the same route without interrail pass is €63:
https://www.seat61.com/trains-and-routes/bucharest-and-sofia-to-istanbul-by-train.htm

The reason why I ask this question, is because If the reservation with interrail Pass is similar to buy a ticket on my own, I will just buy it on my own and save a day.

So my questions are:
1) can you confirm that it is possible to buy Bosphorus Express tickets in Bucuresti Nord?
2) is someone aware about the current Bosphorus Express prices with and without interrail?
3) I will travel From Bologna to Wien (departure 7:45; arrival 17:32) and take connection Wien to Bucuresti (departure 19:42; arrival 15:05 (+1 day)). Does this count as a one day on my pass?


thanks in advance!