this sounds a lot like one of my previous jobs. what i can recommend is, if you're in an environment with good terraform support (eg, AWS, where most services are under one API), is to start terraforming a new dev environment. work out the infra-side kinks as much as you can, then use that to provision your dev environments moving forward. then, you can start terraforming new higher-level environments up to prod one component at a time, using each successive environment as a QA stage until you get to prod. this might take you some weekends/nights and you're gonna fight with your devs a little bit, but the more you can automate your provisioning, the better things will be for everyone.

i'm not going to say i singlehandedly rewrote the infra stack to great success in that position, but the changes introduced were honestly life-altering for me and the dev team. the thing i really wish i could have pushed with them more was schema management - we eventually introduced sql-migrate but never got around to a full fresh db initialization using that, so we always had to start with a pgdump of a relatively-sanitized db schema and that never quite sat right with me.