Gordon,
If your axle plate shows 1500 kg then that is the maximum weight you can use. What happened was that the vans were made with certain ALKO chassis but some were 'downgraded' on the van plate for certain markets. I know when I bought my first Sprinter the brochure stated 1100 kg, but the van plate was 1200 kg. Checking with Morrland revealed the reasoning why, and I was legally able to use the higher weight. I have the 2006 brochure which shows the maximum weight of the 450 TF as 1500 kg. I had been looking at an older brochure which showed 1400 kg. I have the lower grade Samoa 450TF model and this has a maximum wieght of 1300 kg. What made me look at the Samoa was the lower MTPLM, but still the high payload.
As Val has mentioned Moorland Leisure were the main importers, but stopped when Tirus went bust in 2006. They can obviously give advice and may have some parts, but they do not really handle them anymore. However, all is not lost. Tirus made may different barnds of vans and many of the parts were interchangeable. Lunar also sold the Chateau models for a while, and plan to do so again, and these also shared many components with Cristall. However, if you really need something particular you are probably best to head for Holland and find a Beyerland spares dealer.
If the van was supplied by a dealer in the UK then the upholstery will have been changed to UK specification materials. The vans were usually shipped 'sans upholstery' and a UK Company supplied appropriate cushions and logo'd covers. You should even have a mattress and duvet covers all with Cristall logos. We like the mattress cover but my wife baulked at the duvet cover. Yes, the upholstery is high quality and good thick cushions.
The fitting of an aerial was an option, which not many took. As you mention the wiring is all in place in the high level cupboard, behind a panel. and you can fit what ever you like.
If there is a weakness then have alook under the van at your shower tray. You may find like me the drain hole is too large and the plastic tray is unsupported at that point, and like me you may put a big size 10 in the wrong spot, and crack it.
The other weak point is the bottom cupboard in the kitchen unit, as it has a side opening door, not like the 2 drawers above. The hinges can be weakened with travelling and you may have to refit them.
Apart from that it is a great van and we have had ours for 4 years now and travelled all over Europe.