Is there a limitation on how many lookups to be used in tMap as input?
Don't if there is a limit but, the more lookups you have, the less readability is good.
Probably a better practice to have multiple simple tMap (3 or 4 lookups).
I don't believe there is a hard limit. I've never "run out" of lookups that can be used, if that answers your question. In fact, I have built a job that was horrendously busy with lookups that I couldn't add another without it being impossible to see what was going where. Memory will likely become a bit of a problem with lots of lookups as well. How many were you thinking of adding?
Introduction to Talend Open Studio for Data Integration.
Practical steps to developing your data integration strategy.
Create systems and workflow to manage clean data ingestion and data transformation.