Item Long Description- What is maximum number of attributes to compose Long Description?

Summary:

Requirement- 

1) Rule based Long Description Generation 

Situation-

1) Item Class can have multiple Attribute Groups (Example- AG1, AG2, AG3)

2) Long Description is to be Generated using multiple Attributes from AG1, AG2, AG3 

Observation-

1) If we are looking to compose a Long Description with 20+ distinct attributes from AG1, AG2, AG3 then 'Validate' rule throws an error

Questions-

1) Is there a character limitation on 'Return Value' in Rule Set?

2) How can we write a rule to exclude attributes with 'NULL/PLACEHOLDER' values?

  Example- From AG1, AG2, AG3 if need is to use 30+ attributes to compose Long Description and also filter out any attributes with 'NULL/PLACEHOLDER' values; how do we go about doing it?