Rikudo boost and chakra. Casually making 9 Ct each bigger than a bijuu's body.
Rikudo boost is the Rinnegan like Nagato. Chakra? Don't know what you mean. Those CT's were as big as a Biju. Biju size is the same as Jubi's finger. Jubi, Perfect Susanoo and Wood Mokujin are all mountain-sized. Mountain were shown to be equal to fragment of Pain's Chibaku Tensei, whom performed it at his weakened deathbed state.
Rinnegan Sasuke having more Chakra than Nagato isn't backed by anything. Not by hype or feats. Nagato having tons more Chakra is backed by direct statement from Obito. Latter says 1 Rinnegan alone took huge toll on his Chakra and for that reason, he couldn't implant 2. Sasuke has one Rinnegan like Obito, and he keeps it closed to conserve Chakra. Nagato had two Rinnegan open for his entire life and showed no Chakra side-effect; if Sasuke has more Chakra than Nagato, which you describe in a ''whole level'', then there is no reason for him to shut his eye. That's just evidence to keep Doujutsu active, haven't even mentioned that every Jutsu Nagato showed was on entire different scale of Chakra than what Obito and Sasuke have shown.
