I would concentrate first on Terraform and a container engine like Docker to get the project rolling. Applications are configured and containerized using Docker and then provisioned with Terraform. For monitoring, you can use Cloudwatch, assuming everything is in AWS. Your Terraform config files will encode all the server deployments (AMIs, region, etc.). Low-level, application specific config will live in the Dockerfile for each one. And use a git project (or multiple ones) to version and store all of it.

I would actually suggest to involve as few tools as possible to get the job done. Otherwise, you are likely to end up with just as big a mess as when you started. Just what I described above should keep you busy for awhile and you should end up with something serviceable even if it lacks some bells and whistles.