Team building help: Archer and Phainon

Hello everyone! I’m looking for some help from people more informed on the topic than me regarding team building. I have a second account that i wish to play with, but it had only Phainon E4S0 as its limited unit. With that in mind i decided to take Archer E0S0 and Rin E0S0 as my second team, seeing how strong they are as a core. Mind you i do not have sparkle. When it comes to the teams i envision it would be like this:
E4S0 Phainon, E0S0 Tingyun (dancex3 S1), RMC E6S0 (amphoreus LC S5) and E0S0 Cerydra (planning on pulling her in the Phase 2 of this patch)

E0S0 Archer (swordplay S2 for now, Herta LC in the future), E0S0 Rin (Breakfast S5), E2S1 Robin Summeretto and E1S0 Gallagher (QPQ S5)

Now the questions. On his next rerun i’m going to get Phainon to E6S1, in that case would getting E1S0 Cerydra matter or not? Ik that E1 Cerydra is great for him both for damage and QoL for core flame generation but i’m trying to calculate how much of a gain would it be over E0S0 which i’m going to get in a couple of days (hopefully). On the other hand we have Archer and Rin, as i don’t have Sparkle i was debating on whom i wanted to pair them with, and given that Robin is one of my favourite character together with Phainon, i thought getting her to E2 would be enough to make this team work well enough, i know i might encounter some SP management issues but i’m ready for the trade off. Will i pull for Sparkle in the future? It depends, i’m most definitely not getting any eidolons for her if i ever get her, but it also depends on the characters she reruns with, given how Robin is a great generalist support, and her being one of my favorite characters i would be willing to invest in, i thought she might have been the best alternative here.
For Phainon, i’m not planning on getting E0 Cyrene and neither her E2 so keep that in mind, i’m planning on investing on his final eidolons, signature and Cerydra only for now!
Thank you kindly to all those who will answer!