Getting ready for a major software re-do, looking for tips
My iMac's about 6 years old and after babying it along with old FCP7 and an older OS, I'm getting ready to nuke everything on it and start from scratch. I want to re-set to factory condition, wipe and re-partition the drives, and then add a fresher OS and new apps, including FCPX, Motion, Compressor, Garage Band, Audacity, Resolve, FFWorks, A paint program that's not Photoshop, probably Affinity, and a few recreational odds and ends. If I can still keep mpeg streamclip working, I'll keep that too. I hate the current iTunes, so for my music I plan to use SENUTI, I think, and iTunes will just be there for working with the app store.
I think I've already saved-off the videos, text files, documents, images, and music, etc. that I want to keep, to external drives. The most important stuff will get copied back into the new system after the rebuild. I don't use Time Machine on this iMac; instead, I manually copy off things I want to save from time to time, to a usb portable drive.
I believe this machine has a built-in version of OSX used for system re-builds, which is a few versions behind, but I assume once starting from that, it will prompt me to connect to Apple and upgrade automatically, once I've made my various hard drive partition choices. I have a spinning drive and a fusion drive internally. The goal is to run the apps in the fusion drive and keep my media files and etc. on the spinning rust.
I -might- be able to add some RAM; will have to double-check to see if this one has the little hatch on it, and if the chips are still available and affordable along with the software I have to buy.
I'm looking for any words of wisdom and tips to make the overall process go faster and better. Suggested Order of Operations, etc. What are the most common "gotcha's" to look out for?
You haven't really given us any solid technical information about your hardware or OS so I will speculate from what you did tell us. A 6 year old iMac in 2019 would be a 2013 model. Apple's latest macOS 10.14 Mojave is comparable with iMac introduced in late 2012 or later so it looks like as long as your iMac is at least a 2012 you can upgrade to the latest OS.
Since you've already copied off all of the data that you need, I would just boot into the Recovery partition by holding down Command+R while booting and that will allow you to repartitions and reformat your drives using the Disk Utility. Then I believe you will be offered to re-install whatever version of macOS that the recovery partition matches. I'm pretty not sure it will not let you install Mojave so you will have to install a fresh OS and then upgrade it to Mojave.
Having said that, if you can download Mojave from your current OS version then you can make a USB thumb drive installer and use that to go directly to Mojave by booting from the USB thumb drive. Just search for "mojave usb installer" and you will find tutorials on how to do this. This will save you the step of install an OS twice, or maybe in 3 times because I have 2010 Mac Pro on Sierra and I can't upgrade to Mojave, I have to upgrade to High Sierra first and then Mojave. You may be in the same boat if you have to restore to an older OS.
So that would be my "tip". Make USB installer and go straight to Mojave.