FWIW, I've read all the replies, I've just been extremely busy and haven't had a chance to properly address them. This weekend, hopefully, because they're all good and there's lots to think of here.

EDIT: Okay, this is the third time I've sat down to get to these replies. Been a busy week and last night we had to sort out MrsBarn's US Visa, which led to off-topic hilarity at the questions. Anyway, let's try:

First: Ya Kun. Admittedly this is not a stop that's set in stone. I just thought as something vaguely local we should give it a try. On the other hand, it's something we could definitely miss if there were something more appropriate. That said, I found a good article by a fairly well-known SG food author on the remaining Kopitams which suggested Heap Seng Leong on North Bridge Road, which seems like the sort thing we'd want to see. But thanks to everyone on the advice of where to find breakfast and so yes, Ya Kun can be moved around where it fits.

So we don't have a problem with booking in advance, I'll also ask my local friends if they're going out (although two kids so we'll see). But I may make a reservation anyway, just to be safe.
I also like the idea of White Sands, we'll see how our schedule works in the morning but it may be a good idea. It doesn't seem to be much farther in terms of total travel time to Changi Point than anywhere else, and if we get up early we'll be good. I also recall hearing beehoon somewhere, will have to do some reading, but it'll probably go on the list - I want to try it all! Thanks for the suggestions, too!

This wide split of opinions is why I came here for advice! It is also why I haven't fully placed Pasis Ris on the schedule yet. But I'll address this when I get to your last paragraph, which I find very interesting and also difficult to answer.

I really think the New Majestic was a good choice, not only because of the location, and these are all great ideas. KS seems like it may be a more-than-one-night stop based on recommendations.

Now I'll get to the last paragraph later, but first
You can definitely say it's more "chinese-centric" and that's probably very accurate but only because that's the side of Singaporean culture we're most familiar with (due to every Singaporean we've known being chinese and I do proportionally very little Indian cooking at home and almost no Malay). But you're right, this is something we're sorely missing out on and I think that's wrong to do. So I'm going to either try and expand Saturday to include Geylang or we'll shuffle some stuff around on Friday for it. And I'll take your advice on Nasi Rawon, because as I may have mentioned I'm not well-versed in Malay cooking so don't have many ideas going in beyond Nasi Lemak. I may actually put Geylang Market in there in place of Whampoa on Thursday, as it works much better and it's the morning, and also because I love wet markets but MrsBarn may tire of them after the second. So do those when I have some nerding-out time.

and Satay by the Bay - will definitely take a look. I like the idea, how can it possibly be anything but great with a concept like that? I assume it is not directly part of the Gardens by the Bay? So we can bus/taxi/walk there without paying to get into the gardens (I'd rather save it for a different day)

Now the hard one:
Okay, so like any good traveller I want to believe that I'm not typical, but in many ways we probably are. We're not hipsters by any stretch of the imagination, but I have to say that I can appreciate some of the by-products of hipsters like good coffee, small independent shops, and out-of-the-way activities. But style is, to me, mostly meaningless (e.g. the New Majestic was picked for location and amenities, not necessarily the design aspect, which I realize is probably like choosing an electric car because you like the quiet ride and not caring about the emissions or ownership... but yes, I realize it's probably weird). If we couldn't have done the New Majestic, we probably would have stayed at either the Holiday Inn or the V Lavender. Style is secondary, but smaller or independent is preferred. We're also not really "tourists" in that we can skip things like Sentosa or the Flyer or Universal in favour of wandering around Tiong Bahru or even going out to the Heartlands (yes, if we had a week we'd go up to Woodlands just to walk around). But we obviously do want to see a few things just for the sake of getting our bearings, like the quays or the botanical gardens or Mustafa (even though I didn't think Mustafa was "touristy", it just seems out of the ordinary and hence interesting). What we typically want to do in a place is to spend some time just getting a feel for the place, wander around a few local neighbourhoods, and do something unusual to what we'd do in a normal day. Getting lost in a residential area is always an option. Even, for example, going to White Sands for breakfast is fine because even though it's a mall, it's going to have some differences to malls in (as a relevant example) Saskatoon or Krakow. Everything is new, even if it's the same, and sometimes those differences are worth a look. And if they're not, we've got something else on the schedule in a few hours anyway.

Now this week I'm going to budget some time to finish the updated plan (it's now an excel spreadsheet again) and I'll make sure to work these in! Thanks again to everyone!