I'm starting development of a lightning component that will extend functionality of a third party app used in our Production. The 'app' is composed of a dozen or so interdependent managed packages, and is really a full fledged suite built on the SF platform, similar to Sales Cloud or Service Cloud. The component I'm building will be using some of the third party app's custom objects and code/workflows (which aren't readable/editable, but which I will trigger via dml statements).
Another complication is that the part of the app that I'm working with relies on record-based settings instead of straight metadata. Since we have a full copy sandbox available, I can easily mirror the production org settings... but that would not be so easy in a scratch org, I imagine.
I have limited experience with SFDX, and have so far used it for standalone projects which only use homemade custom objects that are easy to pull and push between sandbox/production and the scratch org.
Is it worth attempting to use a scratch org and the full SFDX dev paradigm for this kind of project? I'm concerned about the complexity of dependencies between the many managed packages that make up this 3rd party app.
Is there any reason why I shouldn't attempt to use an SFDX project + CLI + VS Code, but use my Full Copy Sandbox as the destination org for pushing/pulling/testing project components?