I did Paddys , Thetis , Achilles, and Pelion West earlier this year as a circuit.
The track up to Thetis is still there but pretty rough. It comes out between Paddys and Ossa. Chapmans guide book on Cradle / Walls describes where the start of the track is.
As David said good camping below Paddys , also at Leonards Tarn.
My camps were:
Pelion Hut
Paddys Nut
Leonards Tarn
Frog Flats
You could camp between Achilles and Pelion West as there are a few tarns in between, but you would want good weather as it would be very exposed.
The two tricky bits were; coming off Thetis, you need to go right to the western end and find the gully described in Chapmans notes.
Also when you get near the summit of PW and want to get over to where the true summit is, cant tell you the right way to do it , just fiddly. The boulders on PW are very big and it takes a bit of fiddlying around. Once you get to the true summit there is a cairned route along the ridge line until you head down.
Dont under estimate how long it takes to go along PW, it is a long hard boulder hop up to the summit along the top and down the other side especially with overnight packs.
This is not a walk for the inexperienced.
Roger

- Thetis route