On your first point, compression actually makes it very difficult to deduplicate. You may see an initial “smaller” snapshot, but as you create new RARs in the future, it will store much larger chunks of the RAR all over again, since so much of a compressed archive can change in between compression runs. So the net result is larger overall backups. Don’t do this.
You need to deduplicate first, THEN compress - which, coincidently, the latest builds of restic do just that. Compression is now built into Restic going forward. Restic will dedupe and compress on the fly! So use these until it’s in the main branch, and you can have the best of both worlds. 
See this thread for more info and how to migrate your existing repo.