Yes, it what you want, but what about you can afford? You need alloys for ships and you need those anyway so other Empire won't try to eat you. So you always need alloys. But at what moment of time you can afford a specialized planet for it? "Afford" as "can pay for maintenance of such planet it other resources" and as "not forced to build\expand other elements because you also in dire need of those". Basically it seems you have to expand alloy production along with other resource production, instead of living on some initial production and then making a "proper setup" as separate project.