What are the Limitations of Meta Data API in Salesforce ?

You can deploy or retrieve up to 10,000 files at once. AppExchange packages use different limits. In API version 43.0 and 44.0, AppExchange packages can contain up to 12,500 files. In API version 45.0, AppExchange packages can contain up to 17,500 files. In API version 46.0, AppExchange packages can contain up to 22,000 files. In API version 47.0 and later, AppExchange packages can contain up to 30,000 files. The maximum size of the deployed or retrieved .zip file is 39 MB. If the files are uncompressed in an unzipped folder, the size limit is 400 MB. Note the following:
If using the Ant Migration Tool to deploy an unzipped folder, all files in the folder are compressed first. The maximum size of uncompressed components in an unzipped folder is 400 MB or less depending on the compression ratio. If the files have a high compression ratio, you can migrate a total of approximately 400 MB because the compressed size would be under 39 MB. However, if the components can't be compressed much, like binary static resources, you can migrate less than 400 MB.
Metadata API base-64 encodes components after they’re compressed. The resulting .zip file can't exceed 50 MB, which is the limit for SOAP messages. Base-64 encoding increases the size of the payload, so your compressed payload can't exceed approximately 39 MB before encoding.
You can perform a retrieve() call for a big object only if its index is defined. If a big object is created in Setup and doesn’t yet have an index defined, you can’t retrieve it.