Train reservations or wait?

The farther in advance you book, the better chance you have of getting discount fares.

Book the Eurostar at www.eurostar.com.

Book Brussels-Munich at www.bahn.de. Click on the drop-down menu in the upper right-hand corner for English. If you book all the way through on ICE trains, with a change in Frankfurt, the fare is 143.80€. However, if you book Brussels-Frankfurt and Frankfurt-Munich separately, you will pay 96.80€ for the first leg and as low as 29€ (Dauer-Spezial fare) for the second leg.

Use European spellings when booking: Bruxelles, Frankfurt, and Muenchen.

get reservations for both asap.

If you purchase from here, online from the appropriate railroad, you will probably save vs purchasing over there. If you purchase from here from someone like RailEurope, it might be more convenient, but you will pay more than purchasing over there.

For the trip from London to Brussels, you need to go to the Eurostar website, www.eurostar.com.

The German Rail website does not seem to sell tickets from Brussels all the way to Munich, probably because the best way to Köln is by Thalys. So you need to go to www.thalys.com for the ticket to Köln.

Both Eurostar and Thalys have lower priced "promotional" fares for advance purchase.

For Köln to Munich, German Rail has promotional "Dauer-Spezial" fares available for travel through the end of June. Currently, fares are as low as €49 per person, one way, on the fastest ICE (InterCity Express) trains. These tickets must be purchase by 3/31. The Bahn schedule and fare page is at http://reiseauskunft.bahn.de/bin/query.exe/en.

Thanks folks! I will get on it sooner rather than later.

Since Lee mentioned a Brussels-Koeln-Munich route, I checked for fares. The Thalys fare for Brussels-Koeln is 42€. A Dauer-Spezial fare for Koeln-Munich can be as low as 29€. So booking separately and going via Koeln would be cheaper than doing the same and going through Frankfurt as I outlined previously.