Sterling, if you are getting a 250, how much LR?
If like 200lbs or so, then maybe try a blue. Yes, they are more difficult at time to get a good specimen to acclimate. And I never really recommend stars, LOL, but if any tank will be suitable....definitely let it mature etc.
I am a big fan of letting these guys reproduce on their own, personally. That is the best way to add another, and something to really be proud of! So in a tank your size it will come down to personal preference, I think. You will at least, IMO, be able to provide something appropriate for any - though that is a relative thing to say.
THere shouldn't be too much trouble with the other star...is it a Linckia multiflora? I am not sure of the common name and don't quite remember. They are not overly aggressive towards each other - they just eat the same food. In a large enough tank it should be a huge issue.
But keep in mind that around 18 months is the "success" point. They all take about a year to starve. Its hard to know before then how things are going. The risk with two of these stars in smaller tanks, be it Linckia or Fromia or Echinaster, etc, is that they will compete for food. That can make things difficult.