Adding a dimmer to a four-way light circuit
Master dimmer placement is up to your wiring, not your whim
Sadly, for most &quot;smart&quot; hardware (especially fancy stuff that can connect to Alexa etc), the &quot;master&quot; smart-switch or smart-dimmer in a multi-way configuration (such as yours) requires access to always-hot, switched-hot, neutral, and a traveler/remote wire.  This means that your wiring configuration dictates where the master dimmer goes, and in your case, it must go in Box 3, since that's the only place where all the requisite wires are accessible.
That TP-Link can't handle your setup, either, but you don't have to give up on fancy &quot;smarts&quot;
Furthermore, the TP-Link/Kasa HS200 is no good for your application as it can't handle multi-way switching without serious help.  There is no need to despair, though, because there is a way to get what you want, and more, namely the Leviton DW6HD-1BZ.  Not only is it Alexa-compatible, it is capable of not only multi-way switching, but multi-way dimming using matching DW00R-DLZ remotes.
The resulting wiring setup goes as follows:

The white in the /3 &quot;spur&quot; cable gets moved from being nutted with a bunch of black wires to join the existing bundle of white wires in order to provide neutral to the remote dimmers.
Likewise, the black in the /3 &quot;spur&quot; cable gets moved over to join with the existing bundle of black wires to provide always-hot power to the remotes.
The &quot;master&quot; switch gets installed in Box 3, with its white neutral pigtail joining the white wires, its black line-hot pigtail joining the existing bundle of black wires, its red load terminal getting connected to the black wire in the /2 load cable, its red/yellow remote terminal getting connected to the red wire in the /3 spur cable, and its green ground terminal getting connected to the existing grounds.
At box 1, a remote gets fitted, with its black hot terminal connected to the junction of the black wires, its white neutral terminal connected to the junction of the white wires, its red/yellow remote terminal connected to the junction of the red wires, and its green ground connected to the rest of the grounds.
And the other remote gets installed at box 2, wired with its neutral terminal to the white neutral wire, its hot terminal to the black hot wire, its remote terminal to the red remote/traveler wire, and its ground terminal to the existing ground wire(s).

If you decide you don't want smarts after all
If you decide that you don't want Alexa messing with your lights after all, the Lutron Maestro dimmer you picked out will work for your application, using Maestro MA-R, MA-RR, or MSC-AD remotes.  The wiring does work somewhat differently for them, though, as they use a &quot;flow through&quot; wiring for their remotes but do not require neutral to operate.  This permits you to have the master dimmer placed at the box you wish, although with the remotes, it doesn't really matter where the master is.
As a result, we can use the following scheme, with the master dimmer at Box 1 as you desire:

In Box 3, a remote is fitted, with its blue remote terminal connected to the red from the /3 spur cable, its black line terminal connected to the black from the /3 spur cable, its brass load terminal connected to the black from the /2 load cable, and its green ground terminal/wire connected to the ground bundle in the box.
In Box 2, another remote is fitted, with its blue remote terminal connected to the red wire, its black line terminal connected to the white wire, its brass load terminal connected to the red wire, and its green ground terminal/wire connected to the existing ground(s).
And in Box 1, we fit the master dimmer, as you desire, with its blue remote terminal connected to both red wires in the box, its black line terminal connected to the black wire from Box 2, its brass load terminal connected to the black wire from Box 3, and its green ground terminal/wire connected to the existing grounds.

With either set of parts, you can now button the boxes up, turn the breaker back on, configure things as per the manufacturer's instructions, and enjoy your new multi-way dimmer!
Addendum: if you really don't want anything at Box 2
If you want to use the Maestros without anything at Box 2 and with a 3-way switch in Box 3, that's possible too.  You'll want to nut the black wire to the white wire and cap the red wire off in the 14/3 cable at that box, as this will let you wire the master dimmer into Box 1 as described above.  (The reason why I'm not advocating for abandoning the run between Boxes 1 and 2 is to make it easier for someone to put a remote in at Box 1 if they so desired in the future.)
Then, at box 3, the black wire from the /3 spur cable and the black wire from the /2 load cable are nutted to each other and to a jumper (pigtail) going to one of the same color screws on the 3-way switch, while the red remote wire from the /3 spur cable lands on the differently colored screw on the 3-way switch.  (The other same color screw on the 3-way switch is left open; the Maestro, when working with mechanical 3-way switches, uses the switch as a single-pole switch to control the remote wire.)