Hello Harshill,
My answers are based on my experience only, hope it can help you
1.- I think there's no limit of characters that you can store in a Data Item, I've developed a bot that create an HTML file with the report of 10 different applications and the whole HTML was store in a Data Item and everythings works fine. (more than 100k of characters)
2.- It depends on the environment that you are working on. For example, If you read an excel with 30k of rows into a collection it will probably throw you an error "System.OutofMemory Exception" or something like that, so the recommend approach is to read that in small groups and then call the garbage collector, the number of rows to copy will depend on the memory that is available, Ive work in a project where if I read more than 500 rows it crashed, in other project with 5k and there was no problem, so you have to test it.
3.- I think there's no need to write a bunch of characters in an environment variable, but if you ask me I will say the same limit that the Data Item has, none.
May be Im wrong, Im only talking about my experience in development and Im eager to hear different point of view!
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Daniel Sanhueza
Analyst
Deloitte
America/Santiago
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Daniel Sanhueza
RPA Professional Developer
Deloitte