Holland/Belgium Itinerary

This is the first time I've read about a boat stay, but I assume you have the qualifications to operate the boat, and a place to leave it (?) for two nights (?). Because I travel by train, I think of Bruges and Ostend as being very close to each other, and Bruges not directly on the North Sea. Is a canal involved? Are you aware that Nieuwport and Ostend are connected by a frequent coastal tram service?

It's unclear why you are backtracking to Delft. Delft doesn't need three nights, but maybe you're going to adjacent Den Haag, or other nearby cities that you can also visit from Amsterdam. (I haven't slept in Delft, but have been there twice by train daytrip from Amsterdam.) It would make more sense to finish the trip in Belgium, and either hire a car service, or use public transportation (for example, the hourly bus from the Antwerp train station to BRU) to get to the airport. In any case, the train to Ostend will be via Brussels/Antwerp and Bruges. You'll be on a local Belgian train with unreserved seating, from Brussels or Antwerp. I personally consider Antwerp worth more than one night, but that's a matter of taste and travel style.

If you are going back to Delft, you might as well fly back from Amsterdam, it seems to me. I haven't looked at the rail websites, but maybe it's slightly less time to Brussels than back to Amsterdam? But I wouldn't expect it to cost more to fly home from Brussels. Have you checked, or do you care?

Keep in mind that the diminutive size of both Belgium and the Netherlands means distances are quite small as well.
This means you really don’t need to stay at the Brussels Airport the night before your flight because the frequent trains from Brussels Centraal train station to the airport take just 15-18 minutes. In fact, direct trains departing Antwerp Centraal station for the Brussels Airport only take 30 minutes with a train departing every 30 minutes beginning at 4:49am.
One comment on the itinerary- staying in Delft 3 nights and Antwerp one night should be reversed. Delft’s Old Town is tiny with little in the way of nightlife, Antwerp is one of the favorite destinations among Europeans. With a population of half a million and more attractions than Brussels, Antwerp is where I would ( and have ) stay for three nights. It’s a great city to visit.
Another suggestion is to stay in nearby Den Hague
for a couple nights and take the 11-minute train or scenic 28-minute tram from The Hague to Delft as a daytrip.

I would stay 2 nights in Brussels and not near the airport. The museums are great and if it's your last stop, the shopping is great as well. I stayed at the Hotel La Legende, last year. Great chocolate shop across the street and good waffle joint on the corner. (don't bother with breakfast at the hotel).
I loved Antwerp. My fave square in all of Belgium. Loved Deft too. In Delft, I stayed at the Hotel De Koophandel. Very nice room and great breakfast spread. Super nice ladies run the place...so welcoming. I could live at that hotel. It's in a quiet, residential area but very near restaurants on the square. Really loved that place.

I stated at Hotel Grand Canal and enjoyed it. Good location and breakfast.

Thank you all for your help. Any suggestions for resturants in Brussels?