star wars - What was Sidious' plan before the Clone Army showed up? Conquering the galaxy with the Separatists?

The clones were the original plan.

Note from the link you posted:

OBI-WAN: Sido-Dyas. Is he not the Jedi who hired you for this job?

JANGO FETT: Never heard of him.

OBI-WAN: Really.

JANGO FETT: I was recruited by a man called Darth Tyranus on one of the moons of Bogden.

Darth Tyranus was Dooku's Sith name, and Dooku was Sidious' apprentice. QED.