yenwen- IMO you oughta use Klasse All-in-One before their sealant. In the absence of that product, I'd use a wax instead (like theS100).
I'm assuming by "Klasse sealant" you mean the Klasse Sealant Glaze, and not their All-in-One (which is a type of paint cleaner that leaves behind some minimal protection).
And yeah, between the claying and the polishing I don't see any need for a separate paint cleaning step.
I'd expect you to need a milder polish after the PB's SSR2.5 and/or #83. I haven't used the 2.5, but #83 never finished out ready-to-wax for me; the finish always looked better after I went over it again with a milder polish like Meguiar's #80.
For future reference, a decent OTC paint cleaner is Meguiar's Deep Crystal Step #1 Cleaner. Doesn't leave any protection behind the way Color-X does though.