Limit on number of remote clusters in Cross-cluster search

Brief Info:
I am planning to create a multi-cluster (around 50 clusters) Elasticsearch setup to store a large amount of data (around 7 years of enterprise data). This number is based on thorough planning considering the large data set. The data will be spread across all the clusters with multiple indices each, where index names will include the date range of the data it contains.
I have an end-user application that will be used to search for all the clusters. For every search, Cross-cluster will be used to search across all the clusters all the time, where the index names will be used to limit the searchable indices.
A master cluster with zero data indices will be used as a local cluster and all other data clusters will be configured as remote to the local cluster. CCS will be fired against the master cluster.

Question 1: Is there a limit on the number of remote clusters that can be used in a single cross-cluster search? If yes, how can this be modified for 50 clusters? If not, what other approach can be used to search across 50 clusters?
Question 2: What is the most efficient way to form the CCS query that will be fired against 50+ clusters with several indices each?
Question 3: Are wildcards (e.g., cluster-, index-) supported for both cluster and index names in a CCS search query?

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