1. I would say the Armaments use 70% of the original Merge’s power. But Fusion-X could theoretically concentrate the remaining 30% of a Merge Mode’s power into his Armaments to use the full power of a Merge Mode as an Armament if he trains himself to do so.

2. As long as Fusion-X needs them to. So indefinitely in other words.

3. Just in the sense that he can allow others use Armaments as well as other Merge Mode abilities.

4. They can be unless Fusion-X trains himself to use them properly.

5. Yes, as stated before Fusion-X can manipulate an Armaments size as well as many other qualities.