If you want to use a Spirit hub and cranks the disc brake will be on the right hand side of the unicycle. KH frames therefore have the mounting tab welded on the right hand side of the frame.
Oracle frames on the other hand have the brake mounting tab on the left hand side of the frame, so you can’t use that with an outboard brake with Spirit cranks. You could use a Spirit crank with an outboard brake on an Oracle frame if you mounted the brake on the right hand side using a d’Brake adaptor as far as I am aware. You can’t just put the cranks on the opposite sides – the pedals would unscrew unfortunately.
Oracle frames have 100mm bearing spacing on all frames except the 32" and 36" ones which are 125mm. So you wouldn’t be able to use a Sprit hub in an Oracle 32" frame.
Some frames (eg some Mad4One frames) have disc tabs on both sides so you are not restricted to KH frames if you want to use the direct frame mount with an outboard disc.
If you want something that gives you most options for fitting different sized wheels perhaps consider a Nimbus Hatchet frame – you’d need to go with a 125mm hub and inboard disc but you could run that with a wide variety of wheel sizes and tyre widths.
(Edit: The Hatchet description used to say you could run a 32" wheel (maybe that has changed) – however a 32" wheel and Nightrider tyre doesn’t actually fit:
Nimbus Hatchet - Which rim/tire size would you build? - #29 by Tinkerbeau )