A request for assistance from the astro-physical persuaded people on this thread from a terrestrial on-looker.

I would ask that someone shed some light on these questions for me by providing some knowledgable answers.
No trick questions ;o)

I'm trying to get a handle on the reasons why the planets are in their specific locations, or the general theory thereof.

We have gas giants, large planets, and small rocks in our solar system.

What factors are in play to place them where they are now?

Is the ecliptic plane and most planets relative adherence to it caused by a gravitational or magnetic force?

Hypothetically, if we were to change the size/mass of one planet (use Earth as an example), what effect could that have on its orbit and location (distance from Sun) in the solar system?

What effects could a larger planet Earth have on the other planets in this theoretical system?

Appreciate any responses.

Kindest Regards
J.William Dell