How many chemical species are on average in a typical plant and animal cell?
There is no average plant cell.  However this article describes a whole plant flux balance model with 333 metabolites. This won't describe a lot of the molecules plants make.  

I seem to remember a natural product analysis of garlic that had scores of sulphur containing compounds that give its distinctive smell for instance.  This model would be a simplified plant which has no special characteristics like that, which probably doesn't exist.  Its probably not less than half the number of compounds that some plants produce or use.