Congratulations!
Risk: You only need a certificate to steam in public. Testing the engine at home safely is up to you. Consider a hydraulic test, otherwise fire it up with suitable precautions. Safety glasses, screen, water proof apron, mask etc and of course don’t have all the grandchildren next to it. Unlikely to badly wrong, but even small quantities of metal and boiling water flying about might have nasty consequences.
Water: Probably unnecessary to fuss. Tap-water should be fine for a test, unless Cambridge Water is exceptionally hard. Water from a butt will be soft (good for boilers), but may be contaminated with bird poo, vegetable matter, and creepy crawlies. If not clean, filter it. Tumble drier, dehumidifier and defrosted fridge water are also liable to physical contamination. Fluff, dirt from the air etc. Again, filter if necessary. Fill deionised water if worried. Also possible to mix these: a 50/50 mix of hard tap water with butt water will be 50% softer!
Coal: Tricky if you buy it from a coal merchant, DIY store, Garden Centre or garage. It’s because these outlets cater for customers buying smokeless fuel that meets Clean Air requirements. These vendors do not cater for Model Engine drivers, except by accident! Don’t ask for ‘House Coal’, it doesn’t mean ‘coal wot I burn in a grate at home’ – it’s a legally defined type of dirty Bituminous coal responsible for smog. It’s not particularly suitable for engines either. Whilst Bituminous coal is banned, clean, engine friendly hard Anthracite coals like Welsh Steam Coal aren’t, but not many vendors stock it, or sell it in small bags. Here I think the internet is your friend! The main problem is high postage costs compared with a local merchant selling in bulk. Ask your club – they might be organised to buy steam coal by the ton and then sell it in small quantities to members at cost-price.
Dave