>>13813504I'd actually go Surf over Scald.
If you decide to to Expert Belt or Life Orb [and you should LO it up], Surf will give greater returns, esp. on a max Speed/SpAttack Starmie.
If going full offense with Surf, Psyshock tends to be better than Psychic due to being able to get past specially bulky mons while keeping a 90+ STAB move.
If I recall, PWT auto-scales if you're higher leveled, meaning you just EV semi-normally [you're right in that the EV roundings are weird, but just assume that the opponent's maxing out their two big stats].
If you're fine with giving up a moveslot, you could even go Gravity Starmie and run Hydro Pump, Blizzard, and Thunder. I will say though that I've gotten mixed results with it, depending on how much I can rely on having a free turn of setup, but it's an option if you want.
If you plan on going for doubles, I'd run a different moveset for each. Gravity/field effects become a lot more viable and spread moves [Surf, Heat Wave, Rock Slide, etc] reach their best (and need to be prepared for). I'm not as familiar with PWT doubles, so can't help you much.
Honestly, the best thing about PWT is trying out a whole mess of different Pokemon with different sets and trying them out to test their viability and strengths.
I have several boxes of Pokemon that I mix and match whenever I feel like battling the PWT, sorted according to effectiveness.
