Pausanias on Achaean armament, ca. 200 BCE

[Paullus Scipio]

Paul B. wrote:-

As far as I am aware, the general consensus is that Cleomenes only armed his new-made troops, those that end up stationed with him on the right at sellasia, as Sarissaphoroi.

...the troops Kleomenes had with him at Sellasia were all the citizens and mercenaries, while on the other flank his brother had the Perioikoi and Allies.(For a full narrative of Sellasia, see a forthcoming issue of Ancient Warfare)
I do not believe that there is any"consensus" that it is only the newly enfranchised helots who are armed in 'Macedonian fashion'. It is the entire citizen body, and if there is a "consensus" it is this. It is clear from Polybius' and Plutarch's accounts of the battle that the Spartan Phalanx of some 6,000 citizens are formed into a Macedonian style phalanx, and indeed we are told so very specifically by Plutarch.
Kleomenes reforms begin with he and the the remaining aristocracy/homioi donating the land back to the State, and it is then parcelled out into new kleroi to create a new class of Homioi/equals/citizens, as of old.
"......And completing the number of citizens out of the best and most promising of the country people(perioikoi), he raised a body of four thousand men; and instead of a spear, taught them to use a sarissa, with both hands, and to carry their shields by a strap/band, and not by a handle/porpax, as before. After this, he began to consult about the education of the youth, and the Discipline, as they call it; most of the particulars of which, Sphaerus, being then at Sparta, assisted in arranging..." Plutarch: Cleomenes XI

Notice that he 'fills up' the body of citizens/homioi and clearly re-equips them all in Macedonian fashion.....

Later, preparing for his new war against Achaea and Macedon....

"...and making such of the helots as could pay five Attic pounds free of Sparta, and, by that means, getting together five hundred talents, and arming two thousand after the Macedonian fashion, that he might make a body fit to oppose Antigonus's Leucaspides, he undertook a great and unexpected enterprise..."

The total, 6,000, are the total number of 'Spartans' referred to in the sources. All the 'Spartans' at Sellasia are thus part of a Macedonian style phalanx.

That donative of Peltae from Ptolemy comes long after Philopoemen's reforms, so no help in deciding either way for the initial reform

...you are quite right! It is my memory at fault this time - Philopoemen's reforms were carried out in 209/208 B.C.
Ptolemy's gift of "..6,000 bronze-faced shields for peltasts ( Macedonian equipment) and 200 Talents of bronze coin.." occurs in 193 B.C.
However, Plutarch is quite specific about Philopoemen's reforms in 209/208 B.C. - he tells us at length that Philopoemen creates a Macedonian-style phalanx, equipped with Macedonian pikes, and trained to fight close order.
No doubt at all.