Hi, everything is right.

The Interrail Global Pass is your train ticket (don't forget to add the trip zo the pass before boarding).

Some trains requier a reservation, and this is on top of the ticket. Most reservations have a fee.

Exactly what are your worries? That the travel to London, the Eurostar or that the Nightjet isn't covered?

The outbound/inbound rule says can travel of a maximum of two travel days in your country of residence. A travel day is from 00.00 to 23.59 CET, (23.00-22.29 GMT)

Just want to be reassure - I known the rules as you state them are stated clearly in several places. My question was intended to confirm that I was right to assume that onward travel further into Europe via an overnight sleeper is also included. After all Belgium isn’t my country of residence ;-)

Yes, you are good to go. Like Anna writes, in UK you can start 1 houre before midnight, because a travel day is from 00:00-23:59 CET or 23:00-22:59 GMT.

On a travel day you can travel with as many trains as you like and in as many countries as you like. 

This summer my daughter and I travelled from Switzerland, passing both France and Luxembourg on the way to Germany. 9 trains and one train replacement bus in 13 hours.  

Indeed. No problems at all. You do want to print your reservation for the Nightjet though. The attendant usually takes your booking before, or soon after you board. With only a pdf it’s a bit difficult :)