I play a swashbuckler rogue, and I'm trying to maximize my action economy.
Suppose in combat, I don't move and use my Steady Aim bonus action to get advantage on my attack roll (and sneak attack). Steady Aim reduces my move to 0.
Does having 0 movement prevent me from also using Uncanny Dodge (a reaction) and/or Evasion (not a reaction, just a class feature)?
No, Uncanny Dodge and Evasion would not be disabled by the use of Steady Aim. Steady Aim simply sacrifices your on-turn Movement to gain the advantage on attack for that turn. Looking at Steady Aim further, the reduction of Movement to 0 lasts until the end of your current turn. If you were to have some additional feature that allowed you to move as a reaction, you would still be able to do so.
In short, you're good. You are fine to use your reaction to Uncanny Dodge; and, you can still use Evasion should you be subjected to an AOE dex-save spell.
I play a swashbuckler rogue, and I'm trying to maximize my action economy.
Suppose in combat, I don't move and use my Steady Aim bonus action to get advantage on my attack roll (and sneak attack). Steady Aim reduces my move to 0.
Does having 0 movement prevent me from also using Uncanny Dodge (a reaction) and/or Evasion (not a reaction, just a class feature)?
No, Uncanny Dodge and Evasion would not be disabled by the use of Steady Aim. Steady Aim simply sacrifices your on-turn Movement to gain the advantage on attack for that turn. Looking at Steady Aim further, the reduction of Movement to 0 lasts until the end of your current turn. If you were to have some additional feature that allowed you to move as a reaction, you would still be able to do so.
In short, you're good. You are fine to use your reaction to Uncanny Dodge; and, you can still use Evasion should you be subjected to an AOE dex-save spell.