Both 3-Way Switches Upstream of Multiple Split Receptacles
Entering at Switch 2 works...
The good news is that you can bring power in at switch 2 without issue.  The three-way complex becomes an ordinary &quot;spur&quot; setup at this point, with a common wire and two travelers in the cable between Switch 1 and Switch 2, and thus doesn't impose any complications on the rest of the wiring, which looks the same as if you were wiring any other set of half-switched receptacles.
Note that since neutral is available at Switch 2, that covers the 404.2(C) requirement for neutrals to be present at switch locations, so you don't need to worry about bringing neutral over to Switch 1 in this case.
However, your plan for entering at switch 1 fails the Code test
Your problem with your preference for entering at switch 1, though, is that by splicing the neutral from the always-hot &quot;alternate&quot; feed and the neutral that traveled along with the traveler wires together, you've created a parallel, or &quot;looped&quot;, neutral path.  The resulting split in current flow creates a magnetic field between the two wires, which is bad because that field can heat ferrous metal pieces in your walls up like pans on an induction range.  (It's also an EMI  issue, but not one modern gear is susceptible to, due to CRTs being obsolete.)
As a result, the NEC prohibits such a configuration as an effect of how 300.3(B) and 310.10(H) are worded. In order to fix this, you have to bring always-hot to the second witch box alongside the travelers and neutral, which requires a 12/4 cable instead of the 12/3 you were planning on using (or 5 12AWG THHNs in a 1/2&quot; ENT aka smurf tube, if you wish to roll that way instead).  Once you have that straightened out, though, you should be good to go.