If it is a 531 frame I think it will be post 2000. Since they started the TSR range in the mid 2000′s you have to be in that 5ish year gap. I’d guess, from what you describe, that you have an FX8. (It will be if you got that one in Cambridge off ebay very recently)
Mudguards should be available, @£40 from Moulton. Half that on ebay for 20″ currently, might be worth a punt. Not sure about rear racks the but the front racks (if you can get them, there may be a supply issue) can be adapted.
Paint and manual? I’d ask Pashely.