Yes they are excellent, and so are ACME and REE
The thing is that they are extremely well detailed, inside and out
But you need to make sure that they match with the minimum radii on your layout.
The Märklin KKK wont work without interference ;
I use ROCO "universal" at the end of the consist and ROCO KKK elsewhere
And always check wheel spacing.
I also have a few locos from REE and LSM.
All excellent details and beautiful running characteristics but more delicate than the usual Märklin

You can buy AC wheelsets from LSM, Roco or ACME that will fit any LSM coach. You just have to know the appropriate wheel diameter for that model.

As far as couplings, the problem that I have noted is that the coupling shafts often do not extend far enough for the coupler to clear the buffers. I have seen in some older (MG) models that when using Maerklin 7203, Roco's close coupler or even Fleischmann's profi coupler, that two coaches cannot properly couple. The Roco universal couplers have an extra mm in the length of the plug, which means that with those couplers, the couplers extend far enough to attach to the adjacent coupler. If one extra mm is enough, then you can connect one Roco Universal Coupler with a Maerklin 7203. If you need more space, you will have to use a pair of Roco Universal Couplers.
The other alternative is to use a single Roco Universal Coupler and a single Marklin loop coupler, which will also give you enough spacing to successfully couple.

I have also seen similar problems with certain coaches from Liliput (Bachmann), Heris and other brands.

I am very pleased with my LSM models. They are the nicest models out there at the moment.
What I do not like is the fact that spare parts are hard to come by, especially for older models that were made by Modern Gala or are "epuise" according to LSM.

I also do not like the fact that models like the SBB UIC-X were designed with steps that have to be glued in place, while similar DB and other coaches have those parts rendered as integral to the model.

I also do not like the fact that the packaging of most older models (foam) do not allow for the models to be stored with the couplings mounted. This has been corrected on most 2017 and 2018 releases, but is problematic for all models released between 2009 and 2017. I wonder if those 30cm inlays can be ordered as spare parts?

Regards

Mike C