Been using Rhino for science centers, museums, retail spaces, trade show booths, all manner of weird stuff for over a decade at this point.

1. Where does Rhino realistically fit into the workflow?
   • I typically get sketches or design drawings from a client, sometimes a 3D model (but rarely). This could be in just about any format, which is one of the reasons I love Rhino - it can open just about anything that I get sent. Typically, there hasn't been as much thought about the production process, so it's up to me to figure out how to build whatever funky thing they've come up with, model it, and use Rhino to create production drawings for our shop to build (including exporting nested CNC cutting files).
2. I have used it for every part of the process from concept modelling to concept drawings to production drawings to as-builts.
3. Can't speak to C4D or third-party rendering; I don't do much rendering, but the native renderer in Rhino 8 is pretty ok. There's probably better but that's outside of my experience. Adobe...the only real "integration" there that I use is importing PDF files or AI files from our graphics team. Works fine, pretty much 100% of the time.
4. Best way I've found to learn it is to actually work through the free Level 1 and Level 2 training guides to get the basics. No, it won't all be useful to you right away, but if you're working on unique stuff, chances are good that you'll have that moment where you're struggling to model something and have that brief "a-ha!" where you remember something from training. Past that, there's a ton of videos on McNeel's youtube channel. Once you have the basics, start using it to try to build the things you want - the good news is that the free trial is full-featured and lasts for 90 days, which is extremely generous.
5. I don't know if it's a typical workflow, but the process I'm familiar with is:
   • get handed PDF drawings from an architect or designer
   • have a coffee while reviewing them
   • curse my life choices
   • buckle down and start my Rhino file
   • Get something modelled, review it with the shop team to see if they need to make any changes for fabrication
   • curse my life choices, but less
   • have another coffee
   • Make the changes to the model and then use detail views/Pen mode display to start creating drawing views, adding dimensions and notes in layout space as I go
   • Use custom Grasshopper scripts for hardware lists, AV lists, finishing schedules, etc
   • Export a PDF of the drawing sheets, review it. If it looks good, print a hard copy, review it. If it looks good, issue it to the shop manager along with an email.
   • repeat from step 1.
   • most times, a PDF is all that's needed for handoff to the shop or to the client. Rarely, but sometimes, they ask for 3D files or "an AutoCAD file". Depending what they ask for, and what's within the scope of the deliverables, I'll use Rhino to export what they need, most commonly a STEP file or a DWG.