I hate flying, all the security, delays, etc. Would rather work on the train. Eat in the dining car, the food may be lousy, cost high, but you can't beat the view.
I've taken parts of this trip (Basel - London) and if it were me, I would choose the following routing:
- Munich to Frankfurt, probably hourly ICE trains
- Frankfurt to Brussels, I used the "ICE International" IIRC 4 a day
- Overnight in Brussels, I usually stayed in the Ibis right across from the Brussels Midi station
- First Eurostar to London
- Walk across the street from St Pancras (not Pancreas) to Kings Cross and grab one of the services to Edinburgh
I realise I could travel via Paris, but it's an unpleasant station change (Gare de Lyon to Gare du Nord) with suitcases on the Metro.
And by all means, use a Eurail or Interrail pass. Especially in the UK, where the ordinary fares are very high.
Another reason to break your journey in Brussels is that in the recent past there have been some service disruptions with the ICE International where one is cancelled, or departs from Brussels Nord, or worse yet, you need to board a Belgian train to connect with the rerouted ICE waiting in some small station in some small town (forget where, somewhere near Liege) along with hundreds of other irate travelers.
I always felt that the Eurostar should be the first train of the day, as it's a hard deadline and there is no last-minute service as there is with Renfe in Barcelona, Madrid, etc. Eurostar check-in these days is every bit as nasty as in an airport, particularly post Brexit.
For what it's worth, the ICE International trains need to operate on both the German 25kv electrification and the legacy 3kv DC in Belgium, very probably there aren't that many spare trains, so if one breaks down, something gets cancelled.
Frankly, I've had too many cancellations and have given up, but will try again maybe later in the Fall.
The Brussels Ibis used to be fairly inexpensive (EUR 70) but times have changed and it's probably more.
Alternatively, there is Amsterdam, and there is an Ibis right at the station, but it's a longer journey (no cost difference using Interrail) and it's unclear whether the Ibis would be inexpensive.
Last and certainly least, I normally don't reserve seats in Germany, mostly to be able to change plans on the fly when something is late. This has never been a problem for me, but I travel light.
My preference is to avoid night trains. When I was a young man, I would travel to Vienna on a night train, but sleep in a compartment with the seats folded. First class helped here.