I see parts that increase DEFENSE, which is a passive benefit. The only part on page 27 that increases a stat is Anchor Boots: “+3 STR when holding fast”. This would be a judgement call by the GM in the moment.
I think I would rule that POWER needs to be used to activate the boots initially, and once activated we could use contested STR rolls on following turns. If you fail the POWER roll, the STR bonus never kicks in.
Monsters use dynamic rolls for their own attacks against the players only. A player attacking a monster would use the Target Number.
As written, the rules on page 8, excerpted above, indicate that an attack roll using a Hard Suit would require a POWER roll. You may deem it necessary to adjust this, on a situational basis if the narration doesn’t justify it. Maybe a really hard-to-hit foe needs a traditional “to hit” roll, and only after that succeeds a player might exert POWER to use a suit’s part as a consequence of the successful attack.
On the whole, though, I think it’s a fair system: a fully charged suit is powerful and can use all the built-in Height tech to aid in targeting to hit the foe. A suit with less charge may be slower, or re-routing power to other systems, making it harder to aim. Plus, the player needs to decide if they want to expend the limited power for a combat hit.