@Tritonian It really depends on where/how you will end up using the ship. If you end up using it in bounty hunter, it will be very overpowered since the AI doesn't pilot ships well.
On the other hand, since speedy ships (ultralight walls, missile orbiters, etc.) are becoming very popular in modern Multiplayer games, especially elimination & arena, nukes would be ineffective. This is because nukes tend to be very slow, and with good piloting anyone can simply doge them when they are fired.
There is one exception, however. In domination, having a ship in your loadout with nukes will prove very advantageous to you, since playing domination games sacrifices excellent piloting skills for great multitasking abilities. Because of this, people cannot simply maneuver away from nukes with ridiculously fast ships and immaculate piloting. They are also helpful taking down large enemy ships guarding the Alpha spot.
Anyways hope that helped you make a decision on whether you should scale up that 250k ship of yours, and I certainly hope that it answered your first question about whether or not nukes work as a primary weapon.