Thanks for all the great feedback! I'll try to finalise some renders and create a new topic thread in the coming weekend when I have a bit more time, now that I've taken over this project after getting OP's permission.
re: Orange Color
There's honestly many nice shades of orange, and Pantone 151 C is definitely on the lighter/yellower side compared to others, giving it nice summer vibe and would complement on white keyboards well.
I reckon it feels less tiring on the eyes than the more vivid/brighter saturated oranges like RAL 2017 (RAL Orange) or Pantone Orange 021C (basically blood orange).
Another great reference color code is Pantone 2018 C (on page 30 if you have Pantone formula guide) which is a little more vivid/brighter/intense without it being overpowering. So if people want a more vivid orange, I'm considering pivoting to that instead.
re: White Color
I do think the suggestion of a more ivory white like WS4 is worth considering (used to great effect on GMK Violet on Cream, GMK Maestro and GMK Dandy). However I just note that the white here is primarily used as the accent base color, and wonder if people prefer the stronger contrast/punch of WS1 overall in this context. I do see the appeal of a more muted/creamy white, particularly for legends, but just not sure how I feel about it as an 'accent' colour. It worked for GMK Dandy due to it having a muted green. I'll have to mull over it a bit... and try some renders.
re: Manufacturer
Given that it's pretty simple colourway and I'm not doing any fancy sublegends/modifiers or using a GMK stock color, nor do I want to force R5 kitting, I'm leaning towards pivoting away from GMK and going with a manufacturer which can make it a lot more affordable.
The 3 top contenders are WS, KKB and PBTFans. DCX is also an option, but their base kitting is fixed, with nil 40s support.
WS will probably be the most affordable and quickest, however my kitting options are comparatively relatively restricted compared to the other two (less novelties, no windowed keys, and a separate 40s is unlikely), however it has very aggressive pricing.
KKB has the most flexible kitting, but it's a matter of balancing costs.
For PBTFans, I'd first have to convince them to run it, which is probably the toughest hurdle since they utilise a pre-order/instock model, not groupbuy and already have a reasonably long queue I believe. It would be limited to icon only modifiers for bot row too as the community doesn't particularly like their icon/text modifiers. On the pro-side their doubleshot model kitting structure appears to allow for a lot more novelties than WS, they have windowed keys, and the do a 40s only modifier kit, and also split off the numpad from the base kit. The main negative, is that their estimated production timeline isn't particularly transparent as they've shifted to an in-stock/pre-order model (I'm still waiting for a confirmed production date for PBTFans Atomic Purple atm).
DCX is also a potential option, but I don't think Drop is particularly popular around these parts (despite them owning Geekhack lol).
re: Modifier legends
In the context of this design, given the simple mono colourway and nil sublegends, I don't have a particular preference for either text+icon, or icon legends for the modifier keys. It's been icon+text due to the "Harvest" and "C6H8O6" novelties, but now those are cut, there's nothing preventing a switch to icon legends. I should probably create an IC form/poll with comparison renders to see what's the general preference.

Base kit v2
re: Base Kit
This is still in a little flux whilst I figure out the manufacturer. I mean most non-GMK manufacturers have rather similar base kits. It's about the minor details such as including 40s support and alice spacebars that appears to be the primary differentiator.
I've decided to cull the second R2 'tab', as there's no separate alphas kit, and decided to change the R4 1.5u 'Orange' text modifiers back to 'Super', given it's a bit of an extra expense for most doubleshot manufacturers to include these custom keys beyond their default OS legends.
Thanks Fluxius for pointing out the accidental inclusion of the duplicate R1 ~ and R2 \| keys.
I think your suggestion of optimisation of removing accent keys are also good points. I'm highly likely to cull the accent arrow keys (nor don't think they're really worth including them in a separate novelties or spacebar kit honestly). I'm a little bit wary of removing the numpad accent enter despite numpad not being used a lot.
I get that 3-keys 40s physical support in base is not fantastic, but it's a pragmatic compromise I guess when most vendors are not optimistic about a separate 40s kit reaching MOQ. I have yet to decide if I should cull the white accent R2 esc key as well.
(If PBTFans is willing to run this, it would make a separate 40s kit viable, but that kit isn't particularly comprehensive and they don't consider it financially viable to expand it further. WS also appears to have shied away from 40s kits too due to prior GB difficulties.)

Novelty kit v3
re: Novelty Kit
I've culled both 'Harvest' backspace novelties, and also 1 of the white accent novelties.
For now I've also removed the "C6H8O6" novelty for stepped caps lock until I get a price quote that it's worth retaining, despite my heavy bias for it.
I do think 2 full columns of orange slices is probably too much for it to be worth the expense, so I have removed 1 complete column of orange slices for cheaper pricing, whilst retaining enough to abtractly represent the nav column keys.
I think this kit is now as trimmed down as I'd like.