Unique RPG Battling System

Hello everyone! I'm new to Unity and this is my first post, so if it's in the wrong place, please let me know.
I want to create a turn based RPG battle system like this:
Side B (Enemies) Lock in their actions using AI, between attacking, defending, or ready-ing.
Side A (Players side) has three characters, who also get the same options of attacking, defending, or ready-ing.
After everyone has their options locked in, the turn order goes from top to bottom. However:

• If one of the player characters is attacking someone on side B, and side B had the intention of attacking that same player, the attacks collide, and something different happens.
• If the player is readied, this different event happens if they're attacked at all.
• If the player or enemy is defending from an attack, they take half damage.

The "special outcome" has sort of a pop up window where the collided enemies and players are put in sort f a 2-D platform fighter (think Super Smash Bros, but with bullet hell elements) for 3 seconds. During this time, they can do as much damage as possible using different moves, or avoid damage entirely by avoiding the enemy. This serves as a sort of risk/reward, because the potential damage you could take or deal is higher.

Where do I even start with this? I'm a beginner, so are there things I should learn first before tackling this?
Again, if this is in the wrong area, please let me know. Thank you!

 

This is about three or four medium-difficulty problems.

Break it apart: make the combat, show the result, make your second subcombat.

For each of these, look on Google for tutorials. For instance, when I type "Unity RPG system" into Google there are dozens of video tutorials. Work through at least one, preferably two of them, get a feel for things.

Then look up how to make UI popups. Lather rinse repeat. There are tutorials for ALL of this stuff on youtube.

 

Thank you!