This is my first time posting on the Paizo forums, so I hope this is the correct place for this question.
Basically, I am interested in a Siegebreaker Fighter build (with a dip into Ranger or Slayer to grab Shield Slam early). However, I am really confused on some aspects of the build and I don't know if I am understanding them correctly. This build is currently for a third level character (Seigebreaker Fighter 1 / Ranger 2)
Spiked Destroyer
https://www.d20pfsrd.com/feats/combat-feats/spiked-destroyer-combat/
Heavy Spiked Shield
https://www.d20pfsrd.com/equipment/weapons/weapon-descriptions/spiked-shiel d-heavy-or-light/
Spiked Armor
https://www.d20pfsrd.com/equipment/weapons/weapon-descriptions/spiked-armor /
Shield Slam
https://www.d20pfsrd.com/feats/combat-feats/shield-slam-combat/
I plan on using a heavy spiked shield as my main hand weapon. I know that the description says it is an off-hand weapon, but I assume that it does not HAVE to be used as such as long as I am not wielding a sword or something. I would also be wearing spiked armor, which I could choose to attack with as an actual off-hand weapon. My feats would be Improved Shield Bash, Shield Slam, Spiked Destroyer, and Power Attack. Here are my questions about the way this build works.
1. If I choose to use my swift action attack from Spiked Destroyer (after using Shield Slam to get the free Bull Rush) to get a free attack with my spiked armor, would I have to take the penalties from Two-Weapon Fighting since it is an off-hand weapon and I would have attacked with my shield already as my main hand? Or does Spiked Destroyer function a bit differently?
2. What Strength bonus would I add to my shield and to my spiked armor? Would it be my full bonus on the shield as a main hand weapon and half my bonus on the armor as an off-hand weapon? And this would apply the same way for Power Attack?
3. My spiked heavy shield and my spiked armor would both be doing 1d6 points of damage (I am a medium sized creature). And I have to choose to enhance my shield either as a shield or as a weapon. I cannot gain both the AC bonus and the attack/damage bonus at the same time, correct? Is this the same case for the spiked armor?
4. I can do iterative attacks with my spiked heavy shield so long as I do not move more than 5 feet with my Bull Rush attempts, and I can use Shield Slam to make a free Bull Rush attempt on every single one of these attacks? I can only make a swift action attack with the armor once per round though.
5. If I use Shield Slam and knock an opponent prone, when they try to stand up and provoke, if I hit them again with the attack of opportunity, can I Bull Rush them and knock them prone once more before they even stand up? Or would I just Bull Rush them while they were prone?
I am just trying to wrap my head around how this character concept would work. There are a lot of instances were the rules seem to interact in complex ways, which might actually be quite simple and are just going over my head for some reason. But I want to get a handle on these things so that I am not bogging down sessions trying to figure out what I can or cannot do.
Thanks in advance for any help!