What process would you go through for printing on fiber on 16-12 ? Would you l Start with work prints? On fiber, then establish what needs dodging and burning etc before going larger ? Or would you just print on larger ?
My only concern is doing the whole process twice, which takes a lot of time . Is this the way it’s always done?
Outside of a photography course, those who choose to print on fibre are interested in a fine print rather than convenience or economy, so they will tend to be willing to go through several steps. In my experience, work prints on RC paper only give a rough guide to exposures and contrast grades for FB: there will still be some tweaking to do.
Personally, I find it more informative to do test strips on portions of the image at full size, rather than make full-image prints at smaller size first. One factor that seals this issue for me is that even with Ilford papers, there are batch variations between boxes, so your box of 10x8 may not give the same results as your box of 16x12. In addition, as Matt King said, the aesthetics change as you change print size - so even if you up-scale your exposure times, you may find them unsatisfactory given that the elements of the image are now bigger. You may also want to change the contrast by half a grade.
For all these reasons, I cut up full sheets into test-strip sizes. It seems wasteful, but the alternative works out more wasteful in my experience.
I think you also asked about processing FB prints at home? Yes. If you can claim use of a bath for a few hours, you can produce fully archival FB prints. Put a board over the bath leaving access at the tap end. Your trays go on the board, and you drop the fixed prints into a bath-full of cold water. At the end of your session, replace the plug with a short length of PVC tube with a few holes drilled in it. That will allow you to leave the water running gently so as to keep a through-flow. I processed my prints like this for many years. Message me directly if you want more detail.
As for drying: hang them up or place on screens if available. Once they start to feel crisp rather than limp, you can stack them and place under a sheet of heavy glass (ask any glazier for a scrap sheet of safety glass, and if you feel cheeky, ask him to smooth the edges too). It takes a couple of weeks to fully flatten 20 prints, but less time for a smaller stack. The only ways to stop them curling slightly afterwards with changes in humidity are to store them under pressure, or to dry-mount them.
Good luck!