Hi!

With either set you can connect the lamps to the car frame. Depending on your digital controller there will be more or less flickering of lights when connected that way.
60923 will be hard to get - and difficult to program with an MS1. The current set would be 60943 plus 60942 - easy to buy, but also difficult (or maybe impossible) to program with an MS1.

There should be no problems programming the basic features (e.g. motor parameters) and using a 54631 with an MS1.

The RRP for 60923 is Euro 129.95. The RRPs for 60942 and 60943 are Euro 39.99 and Euro 29.99.

With 60923 you get a decoder with cables and solder the decoder into the loco. Thus you cannot upgrade the decoder.
With 60942 you get a circuit board and the decoder will be plugged in. Thus it can be replaced later on.

ESU 54634 (RRP is unknown, but many dealers sell it for less than Euro 45) also contains a circuit board.

If there is enough space in the loco, I try to use a socket for the decoder so I can replace it easily.

With respect to MS1, the 60942 could be a problem (I'm afraid you cannot program that thing with an MS1).
The 60923 decoder can be programmed with an MS1, but a trick is required.
There should be no problem programming the basic features of a 54634 with an MS1.

The older ESU 52634 also has a circuit board. It includes a V3 decoder and there should be no problems programming all features.

The ESU sets come without mfx.

The Märklin sets supports mfx - and that's why they are so difficult to be programmed: the MS1 cannot easily program mfx decoders.
The motor may work fine with the default settings, so maybe no programming is required.

I understand that postage costs are high for you when you order from Germany and thus it's nice to be able to get items locally.