(C) Equip only to a Warrior-Type monster that is the only monster you control. (1) It gains 300 ATK. (2) During your Main Phase, you can send this equipped card to the GY. If you do, the equipped monster can attack twice during the Battle Phase this turn.
The (C) Condition is not an effect, it can't be negated.
If "Assault Armor" is equipped to your monster, then after that you Summon another monster, "Assault Armor" remains on the field.
The requirement that you control no other monsters only applies to equipping "Assault Armor". If an effect is chained to "Assault Armor" that makes the target no longer a Warrior, then "Assault Armor" cannot be equipped to it, and is destroyed.
The (1) Continuous-like Effect applies while this card is face-up and Equipped to a monster.
Equip Spell Cards continuously target the equipped monster.
The (2) Ignition-like Effect activates & resolves on the field.
Sending this card to the GY is a cost. This effect can't activate while Macro Cosmos is active, since you can't pay the cost.
This effect does not target.
Sending this card to the GY is a cost to activate the effect to attack twice. Activating this effect starts a chain. This effect does not target.
If "Assault Armor" is equipped to your monster, then after that you Summon another monster, "Assault Armor" remains on the field. The requirement that you control no other monsters only applies to equipping "Assault Armor".
If an effect is chained to "Assault Armor" that makes the target no longer a Warrior, then "Assault Armor" cannot be equipped to it, and is destroyed.
If the equipped monster's type changes after "Assault Armor" is already equipped to it, "Assault Armor" remains equipped to that monster.
You can only send "Assault Armor" to the GY to activate its effect during Main Phase 1.