Random thoughts -
My older Allmand 5KW Allmand generator has bearings on both ends with a LoveJoy coupler to the ST2. It has been a reliable runner for several decades. One of my Winco generators will fit up to the adaptor housing, although the bolt pattern is different and the rear mount support is in a different location. Center it very carefully, transfer drill, and tap the holes. Then spend whatever time it takes to get all the metal shavings out before you start the engine. Flinging tiny hot bits of metal through the air shroud and around the shed while you are trying to test the generator output lessens the fun considerably.
Yes the ST is a smooth runner, but it is noisy. It sucks a lot of air for cooling, and has no water jacket to absorb noise, and runs at 1800 RPM. The factory muffler is a bit of a joke, it does little to lessen the noise level and is in just the wrong place to walk by without burning your leg. An aftermarket muffler from a Ford diesel tractor reduces the noise level a lot and can be routed out the shed. With a little work and a heat shield it is also a lot safer to work around.
The CS has many things going for it besides the obvious cool factor. It is a slow, massive engine that will last most of forever if maintained. That is the Lister, I don't know about the Listeriod. But it is not the most fuel efficient engine Lister made.
An engine shed is different things to different people. I have seen one where a wall had to be removed to work on the engine, and also one that was a workshop with an engine in the corner. I can say that some thought needs to be given to your needs, wants, and money before starting on building. I started with a metal building from a big box store. With an air cooled engine inside, this added the boom to boombox. The sound I was trying to contain made the walls into a remarkably effective echo chamber. So I insulated the hound out of the boom box. That worked great, but when summer came the inside temperature rose to astonishing levels. An air cooled engine requires an amazing amount of air for cooling when the ambient temperature is over 105 degrees. At that point my wife got a nice gardening shed and I started with a larger stick built home for my engine and workbench. Six inch walls with fiberglass insulation and OSB plywood abate the noise quite well, no ceiling and a thermostat controlled fan move enough air to cool as needed. The engine puts out about as much heat from the exhaust as it generates in usable power, so that needs routing through the wall. It also gives off about as much heat to cool the engine, and that needs a way to out of the building at least in the summer.
I put my engine on a concrete base, for the sake of tradition and to make it easier to work on. At my age getting up from a crouched position is a chore, and reaching out to a running hot engine to lever myself up is not a good plan. Building a solid engine base with concrete is easy and cheap. It may be more a reflection on my welding skills, but I passed on a metal base. This way nothing vibrates apart, and it won't tip over.
As to loading factor - a diesel seems to like a good load. To me this means working out in advance my needs for the system. I use my generator as backup rather than my primary power. So I toted up the real load required, and planned out the amount of power required to size the system. The ice box, some lights and a little air or heat is enough to keep the wife happy. Central air is out, if nothing else that much load turning on and off makes the power load difficult to predict or control. This way I can run two small window units in the summer, and electric space heaters in the winter. Load shedding systems can do the same thing, but this is a simple backup system for me.
I would say the ST is a great first generator, and if you can get one for 500 or less then I would. But this is your money, you should take all advise with a grain of salt and make your own choices. Whatever you do, someone somewhere probably won't be happy. Try to make sure it isn't you...
