With regards to the Exoslides, how are you planning on implementing them? I’ve played around with them a bit and they’re probably well suited to something long like yours but I don’t love them. They’re 80mm long, which is a potential problem as they add considerably to the size of a traditional printer (not an issue with yours) and they’re more expensive than other approaches for linear movement (but would be cheaper than linear rails in an application like yours). The big thing I didn’t like about them is that they work best when four are used to a rail and that complicates things like cable management (can’t have drag chains with them).
I’m curious, how are you keeping sag in the middle (I think you have a fair amount of mass on your gantry, if I remember correctly, you’re putting your spool on it) to a minimum? Are you using something like 20x40 or 20x60 V-Slot for rigidity because I know you’ll get a noticeable amount of sag with basic 20x20.