[Alneyan]

Why would you want to stop at 3 miners? With a standard base, you can reach four miners (each at 100kt), and it would be possible to go from one to four in two retrofit steps.

It would be much more profitable to put as many miners as will fit, either by building the base directly, or through retrofits, since a single miner isn't enough to give you enough minerals. A ship might be a solution as well, especially if you already have Battlecruisers or above; ships cost more in maintenance, but you do not need a mobile Spaceyard to produce them, and they can travel at an amazing speed of one, even without supplies (if, for one reason or another, you need more speed, a few Solar Collectors should do the trick. Or more than a few).

The final output of your remote-mining operation will mostly depend on the resource value of the planet in question, and you should focus on these 150% and above resource values. Tiny, small and possibly medium asteroids are the most valuable for this purpose, since they are unlikely to bring more if you were to shape them into planets and colonise them. Larger planets should be transformed into planets though, as planetary-based mining is more efficient than remote-mining in this case. If you have already shaped the planets, you should leave out breathable planets as well; but there are easier things to predict than that.

Later on, *big* bases could be another solution, with twenty miners or so. These will give you an impressive boost to your resource income, and only big breathable planets will be able to rival with these remote-mining starbases. At least, you will still have a few asteroids about, rather than an uniform Empire full of transformed planets everywhere.