I've been down this road.
Leopold is the most rugged of the pre-builts, and stands up well to modification.
It can also be quieted somewhat, or at least given a relatively deep and consistent sound profile.
I had a stock [MX Brown] Leopold FC900R PD modified into a keyboard with 62 G Aqua Zilents:
https://geekhack.org/index.php?topic=103412.0The 'surgery' worked, and I was able to get the LED colour changed to one of my preference.
You don't notice the prominent branding so much, if you have good keycaps.
Sound-wise, the keyboard is not what I would call "mute." The Zilents still make a (muted) impact noise. The switches themselves are not perfectly silent.
In stock form, the board had an inconsistent sound profile. Some parts of the board were deep and thocky, others were just plain clacky or loud. The spacebar was mondo loud.
With careful lubing of the stabs, some lube applied near some noisier switches, adjustment of the stock dampening material, the board sound profile became more consistent. It's possible to quiet the spacebar on Leopolds, it was done with 2 of mine.
I'm right-now thinking of having the board resoldered with Boba switches. Here's why:
The U4 Boba switches are quieter than Zilents [and cheaper], and have a less-steep tactility. If you already tried and like Zilents, go ahead and build them. But the U4 Bobas are more like Holy Pandas in tactility, with a slightly mushy bottom-out.
They are intended for modders / customizers, and friendly to a wide variety of spring weights. They also don't need much lube. You can buy them in pieces, for easier lubing and assembly.
If it's more of an MX Brown / Clear tactility that you're looking for, just put Silent Sky stems in the Boba housings. You can dial the weight back to 55 G, and have a quiet, light switch.
If I were in your position, I would build a Boston or similar keyboard with Boba switches. A modded factory board probably isn't going to be as easy to quiet as a custom. You can add dampening materials to your heart's content.
So here's some points:
-Leopold most rugged pre-built. Takes well to modding. Hard to desolder because they don't go cheap on the soldering. Kind of noisy from factory, but can be quieted a bit. Zilents will work fine in them, but Zilents aren't the quietest tactile.
-Varmilo makes great keyboards. You can even order it with Zilents from the custom store [in some sizes]. The full-size isn't low-profile, only the TKL. I find that the spacebar stabilizers don't hold up over time as well as the Leopold's. Varmilos are also probably harder to desolder and resolder because of internal layout issues, from what I've heard. Leopold might be better for modding, Varmilo probably nicer in stock form.
-A large custom kit will give you the best options for switches and silencing.
-Have you considered the KBD8x mkii? It's a TKL, but you can also buy the numpad separately. KBD8x mkii can be silenced very well, from the videos I've seen. Look them up with Silent Alpacas or other silenced builds on Youtube. You can use a variety of dampening materials, including a stock one that you can order with it.
BTW You WILL have to lube your switches for best results, and that includes Zilents. I don't see many people going to the trouble / expense of building a Zilent keyboard, and not lubing those switches.