I am not aware of any OFFICIAL limits.
However, I just crashed v9 SR5 by intentionally constructing hundreds of lines of +sum(value)-sum(value). And I was able to crash an earlier version when I tried something similar about a year ago.
So it is possible to hit a limit of some sort. However, I've not heard any reports of similar crashing with ACTUAL large expressions used in the real world, and I believe there are people out there with expressions hundreds of lines long, possibly thousands.
