What potential allies? Bide our time for now, but if they send ships toward Sol, blast them, then camp the jump point. If they're stupid enough to use the gate for military transit, it shouldn't be difficult. If/when we've built up our own forces, smash their fleet and take their homeworld. To that end, I suggest developing boosted radiation output warheads, a missile for them, and a fighter to fire them.
I disagree. If you want to take and keep their homeworld, it helps if they're not all dying of radiation poisoning. Yes it makes it easier to hold it, but they you have to deal with a very protracted campaign of freighter-hauling everything to a world that isn't blanketed in nuclear winter for the next century.
Who cares about their homeworld? Why would we take anything there? Radiation-boosted warheads do less damage to industry, which means most of their installations will be taken intact, which will boost our own development and expansion. We get their wealth and surviving ships and shipayrds regardless of how many of them survive, and once we've taken everything off, all we have do to is drop some garrison battalions on it and collect taxes until they all die or the radiation dissipates. If the former, then their population builds back up and increases our tax base. If the latter, then we have an empty 0.00 cost world to settle.
If they join us, we have 38 meatsheilds to sent first. if it works that way.
I have never seen an NPR become friendly enough to ally, am not sure if it is even possible, and even then they would only engage enemies that they came into contact with. Quite apart from that, NPRs develop notoriously slow, so they would be sub-par meatshields at best, and would likely go down to Invaders without doing any real damage. In the meantime, during those long decades where we try to befriend them, they're sitting on a warp line that could potentially yield valuable worlds and/or resources.
Therefore, my vote is that we befriend them like Takamachi Nanoha would if she were a Space Marine.