CAAD Beater: Single Speed to Geared

Intended to be a reliable/nippy commuter, I purchased this a month or so back:

https://www.lfgss.com/conversations/354698/

I’m now in a position where I barely need a commuter, but could do with a bike to hook up to my trainer for indoor training (would rather not use my TT/“best” road bike on it). I know the easiest solution would be to flog this, and sort a cheap geared replacement, but how easy would it be to re-convert back to how it used to be?

Thinking out loud, I’d need:

• New BB
  
• FD/RD
  
• Shifters
  
• Cassette (+different rear wheel hub?)
  
• Maybe chainset (although on ERG mode the current one should suffice, and also preclude the need for an FD)
  
  

Any help/guidance appreciated. I’m essentially trying to work out if it will be cheap and straightforward enough (my skills/tools are limited) to make it worthwhile.

Thanks,

Lewis