If it were me
The A4000 is awesome, as you say a keeper.
The A1200 would be great as a WHDLoad machine with one of Jens new Accels. (Fit 4gb CF-IDE and sell the overdrive)
You could keep one of the A600's without floppy and fit Jens ACA630, Indi ECS and A603
Keep one A500 for nostaliga and old Floppy's
Sell the rest to partially fund the upgrades
Although it might be nice to keep the CD32 as well if you can get it going...