CoH has too low sinergy with Yellow Chakra so I'd use that GCD on another strong AoE Heal, like BH or even a good targeted PoH (Low sinergy too, sadly). You can find some logs from high-end holy priests on 10m without a SINGLE CoH (on every encounter).
About refreshing Renew, you cast it on your buddy (low duration, glyphed) then you just single heal him to refresh that Renew and extend it to max duration (like without glyph). Faster you do it, easier will be to keep 2-5 rolling. Quality of Life tip