5e knight: Fighter subclass

[Zhorn]

Martial prowess
At 7th level, your martial skill is unmatched, being able to use your shield offensively and your great weapons defensively. You gain the following two benefits.

Shield bash: While wielding a shield, whenever you take the attack action you make a single attack using your shield in addition to your normal attacks. You are proficient with this attack and it deals d4 + your strength modifier as bludgeoning damage.

Parry: While wielding a two-handed melee weapon, whenever you a make melee attack roll against a creature, hit or miss, you gain a +2 AC bonus against melee weapon attacks made from that creature until the start of your next turn.

I like the ideas of these, though I'd be inclined to tweak them slightly:

Shield bash: While wielding a shield, whenever you take the attack action you can make a single attack using your shield as a bonus action. You are proficient with this attack and it deals d4 + your strength modifier as bludgeoning damage.
^ line it up with the same form of action economy as TWF or PAM

Parry: While wielding a two-handed melee weapon you gain a +2 AC bonus against melee weapon attacks made by creatures within your reach.
^ less tracking involved.

Now questions about shield bashing:

• Would shield bash's to hit and damage rolls be modified by a +1/+2/+3 shield?
• Would a modified shield (MM p204: Lizardfolk's spiked shield) override the 1d4 bludgeoning damage?
• Does treating a shield as a weapon negate the Dueling fighting style?
• Is treating a shield as a weapon compatible with the Dual Wielder feat?