I’d say you’re on a good path already! A couple of initial thoughts:
For the Gateron Yellows, you may want to consider the Pro Yellows. They’re identical in price and offer excellent performance for what they cost. Since you mentioned Divinikey, they have the KS-9 variants in stock (they’re out of the milky ones, unfortunately but I’m sure you can find them elsewhere).
For lubing switches, do you have the other helpful accessories? I’m thinking a switch opener, a fine brush, and a prong holder would be helpful. You can also use the 205 to lube your stabilizers, if you feel so inclined. That said, the Pro Yellows come with lube applied from the factory so this may not be absolutely necessary.
Keycaps quickly get into personal preference territory but if you get caps that are a bit thicker, that’ll likely lend itself more to the sound profile that you’re looking for. You shouldn’t have any issues with compatibility since you’re looking at a standard 60%. As a general rule, ABS shines more readily than PBT.
I’d echo what @leemu said about the accessories; it’s definitely worth picking up a switch opener if you plan to tune them. Brushes are generally nice and cheap.
Most places will sell jeweler’s claws as stem holders - and they’re fine for that purpose - but my favorite thing to use are the 4mm mechanical pencils that are also sometimes sold as stem holders - they more or less cover the cross-mount when holding the stem, which is great for my not-so-steady hands.
Generally, taller caps will give deeper sounds compared with shorter ones of the same material. Softer plastics materials tend to give deeper sounds than harder ones of the same thickness - this is especially true for plates.
If you can spare the width of one more column and are considering a GK61, you might save around $25 with one of these, available now, or another $5 with one of these, available later this month I think. Both are vendor-specific versions of the CIY Tester68.
On the other hand, there’s a lot more aftermarket support for GK’s and for 60% in general - if you stick with one of those, you can always upgrade the case, plate, etc. later. I think with those Testers, there isn’t much to do with them aside from improving the stabs and possibly modding the battery type.
Switches that are properly lubed by hand will almost always be better than what can be done at the factory. That said, the factory lube on them is pretty good and I’m thinking that you could instead use that bit of your budget on something else, like keycaps. I’d say find keycaps that you like and then work backwards from there. If you have budget left over for lube and an opener, go for it. If not, then it’s not a deal breaker (in my opinion).