There are a lot of things that you would need to add to your business cards in order to make them worth your while, and perhaps the most crucial thing that you would want to focus on is making it so that the text is as visible as possible. Choosing the right font is definitely going to be important in that regard, but you should know that the size of the text tends to matter a lot more than you might initially be capable of realizing. This raises a unique issue, since you need to figure out what the best text size might be based on all of the relevant factors.
It is quite common for people to go overboard with the text size for their Metal Business Cards, and that can be problematic since it would restrict the amount of space that you would have. There are likely going to be numerous bits of data that you would like to include, so reducing your text size can be a useful technique for making that happen. Bear in mind that making the text far too small could potentially make it illegible, thereby defeating the initial purpose of the card itself.
We would advise you to find a middle ground in which the text is small enough that it allows you to pack in all of the necessary details, yet large enough to be clearly visible to anyone that sets their sights on it. Try to experiment to see which size ends up catering to all of these disparate needs. It might require some trial and error before you can make a decision that is final all in all.