There's no main phase between your combat phases, so you'll have no opportunity to cast spells or activate abilities that could only be activated any time you could cast a sorcery. For example, you won't be able to cast another creature or activate Hexplate Wallbreaker's equip ability between combats.

If you attack with multiple creatures equipped with Hexplate Wallbreakers in one combat phase (or one creature equipped with multiple Hexplate Wallbreakers), you'll have that many additional combat phases, but your attacking creatures are untapped only during the current combat phase.

If the ability causes two Rebel tokens to be created (due to an effect such as that of Mondrak, Glory Dominus), the Equipment becomes attached to only one of them.

The Rebel enters the battlefield as a 2/2 creature, then the Equipment becomes attached to it. Abilities that trigger when a creature enters the battlefield see that a 2/2 creature entered the battlefield.

If the Rebel is destroyed, the Equipment stays on the battlefield. Similarly, you may pay its equip cost to move it from the Rebel token to another creature you control.

Once the equipped creature attacks and the triggered ability resolves, you get an additional combat phase even if the equipped creature doesn't survive the first combat phase.

Untapping an attacking creature doesn't remove it from combat.