Hi Ian, welcome to the forum and the wonderful world of CNC. Looking at what you are planning to do I suggest that diving in with a rather expensive CNC mill is perhaps not advisable. You may be much better off starting with a cheaper manual mill to start machining your castings, to learn about things like workholding, feeds and speeds etc. Depending on what you are making a lathe may be useful too or even essential. Also, by starting with manual machining you avoid at least one layer of learning until you know better what you are trying to achieve.

Could I suggest that you look at the Model Engineer forum https://www.model-engineer.co.uk/forums/ ? You'll see a lot of useful information (and some dross) and it's a great place to ask questions. One member who posts as JasonB (Ballamy) uses CNC a lot in making model engines, including the manufacture of "castings" which are designed in 3D CAD - that's another angle that you could find interesting for the future. You will also see a couple of books advertised, one by Jason on milling technique another on turning (if you're interested). There are some useful suppliers there too - one I can recommend for machines is Arc EuroTrade who are based in Leicester, who sell and give good support to a range of Chinese mills and lathes. At one time they sold two CNC machines, the SX1 and SX3, which are reasonably good - worth looking on the s/h market. JasonB uses an SX3 to very good effect.

I have a Denford CNC mill - a Novamill. This is rather tiny but very nicely made. You could look out for a Denford Triac which is a bit bigger, used ones come up on eBay from time to time. If you are lucky it might be without the electronics - they are rather old and the mechanics is worthy of fitting modern electronics (from the likes of JazzCNC for example) - which would make it cheaper and better than the original. My Novamill was about £600 and I built the electronics for less than 200 (but that's my trade).