A HT1 CA is doable. It just doesn't have the speed advantage to close with a HT3 CA and its SM, W, Z and D advantage.
It's doable, and in my opinion, not necessarily a horrible idea. Especially given the fact that by the time the proto-type launches, the Tarek will likely have better tech to install on her.
The Coalition is in a tough position here. Its government is philosophically opposed to launching an 'unprovoked' attack on the Tarek. It's too loosely organized, and its states have too much veto power to do something that doesn't have near unanimous approval like that. And there is nothing like unanimous approval for a pre-emptive attack, no matter what the Wunderlanders think. Dealing with Russia is different, as there is a long history there, and close to unanimous agreement that they don't want to be conquered or marginalized by the Russians, and agreement that if they take their eyes off of them that's exactly what will happen. With the Tarek, and other extra-solar races, the situation is very different.
Privately, the current administration's attitude towards the Tarek is much the same as the last administration's attitude - leave them alone and hope they stay to themselves. Protect the Wunderlanders with whatever ships can be spared, and retaliate with overwhelming force if the Tarek attack.
Kurt