You'll be able to build a CNC router capable of machining aluminium for about (ballpark) the same cost as CNCing a reasonable size mill. the X1 size of machine sounds too small for your needs, sounds more X3 sort of size so you're looking at £1200 or so before you start. You'll still need to add ballscrews/motors/drives and like all things retrofitting to an existing table involves some machining operations that are hard if you dont have somehting to do them on to start with (or £2000+ for the commercial kit). Bootstrapping a new build is much easier IMHO. By all means consider an X1 to help build the bigger machine and keep it as a manual unit for those small/quick jobs where setting up the CNC is overkill.