You should be able to make ICE 19 leaving Brussels at 18:25, e.g.:

Or you go via Köln Hbf to Düsseldorf (ICE 619 does not call at Köln Hbf today because of engineering works):

Further, it's much better to use the DB Navigator app: it is more up to date and uses realtime data and should also display platforms and platform changes.

In Brussels, when arriving with the Eurostar, there is a short-cut to get to the other platforms faster, see this page.

In ICE 19, there are still plenty of seats available. Coach 22 still has the most:

So just go there and find a free seat.

If you miss ICE 19 at 18:25, then this is the next connection to Düsseldorf:

No reservations needed. In IC 517, take a seat in one of the last coaches, since the station tunnel in Welkenraedt is near the rear of the train.

In another word if i am able to make it for ICE19, i just would have to hop onto the train & find the seats without having to pay for anything? Meanwhile i would need to add the trip to my mobile pass. 

So you have next train suggestion that i should take this train if i were to miss taking ICE19 ? 

Also, does all train departure requires all passenger to arrive 90-120mins prior to departure or is just the Eurostar thing ? 

Correct.

Correct.

That's a Eurostar thing (who don't like that either but it's imposed on them by mainly the British government). In France, the departure process starts 2 minutes before the published departure time. And as always, in big stations, take a few minutes extra because you may need to walk to the other end of the station.

i see. 

How about this next train leaving midi Brussels ? 

That's the same one that I posted in case you miss ICE 19 :)

@rvdborgt 

ah i just saw it. 

Thank you so much for being a life saver

Additional: the overnight ICE 619 stops around 20-25 mins after DUS at KÖln MESSE DEUTZ, which is a rather stark empty stop just across the river from Köln HBF=Main. You do not have to go to DUS and come back same sector, there are trains ev. minute or so from HBF to Messe )take the S-bahn), this may save you more time. NOTE this is an only seats normal daytime ICE and it stops quite long at FRA-airport in the mid of night-DO take care of belongings there!!

IF you need to stock up: In K-HBF are at least 2 smallish convenience supermarkets (REWE toGO) with even fairly normal city prices and open 24 hrs. After arr in MUC same chain-just beyond the escalators going down to S-bahn, far left side.

Seeing your name: by now about any major HBF in nearly all German big cities have a Asia-HUNG noodles/rice shop-but not 24 hrs open.

Today it doesn't.