I do not have much of a problem with the welding or the earth construction, let me explain.
The earth construction and sub launch is not a problem because they have warp drive. Who I am to second guess a culture like that. If they find it more economical to build on the planet and then launch so be it. Same goes for 'welding', thet have warp drive, how can we second guess that.
Maybe they have the orbit teather in star trek and they just pull the loads up via the rope. Who cares.
Now as for the micro-welding, we have no idea. A custom paint shop will paint your car such that the paint forms one solid molucule of paint around the entire care. The same priniple exisits for metal. You fuse the metal on the sub atomic scale such that there really is no 'joint'.
Over all I see no problems... i may be blinded by darkness and giggityness though.