DB22 Build Questions (1st time builder)

Just gonna preface this by saying some of these questions may be dumb, so bear with me. I just started working on my first 3D2A build (Fl-Eggs DB22 replica) and I've got a few questions that I've been struggling to answer with readmes and forum posts alone. I understand this might not be the best starting build to get into the hobby, but I've always had a passion for engineering and I'm willing to take on a challenge. I also figured .22lr would be safer in case something goes wrong.

I haven't purchased an upper reciever or .22lr BCG yet, and I'm planning on making this a dedicated .22lr build. Do I need to purchase a complete Mac11 upper, or are there a few specific parts I need? I'm planning on purchasing parts from Velocity Firearms, but any recommendations for where to buy would be great.

Is there an updated TURD I should be aware of, or should I just use the one included with Fl-Eggs' build pack? Also, are there any other recommended FRTs for this build or is it just the TURD?

I'm currently printing with Polymaker PLA Pro, are there any parts of this build where I should look toward a stronger material? I have an Elegoo Centauri Carbon, so I should be able to print CF filaments (haven't tested it yet though).

Are there any general things I should be aware of when assembling/fitting parts? Especially the barrel, I'm most nervous about that part.

Once again, thanks for putting up with my questions. I'm super excited to start diving into this hobby!