If you have the stock gift module ( Basic is all that is needed), then you can enter as many stocks as you want on one gift. If only one fund is involved in the gift, there will be one distribution line filled out on the gift and one entry on the GL account tab.
You can only have 5 different funds associated with any gift and stock gifts are no exception to the rule. It is extremely rare than more than 2-3 donor funds are involved in a gift of securities.
If there are 20 stocks, if using the stock gift module, you will have 20 positions that can be sold or retained and they are managed independently of each other. (20 is just an example- you can have as many as necessary)
If you don't have the stock gift module, then you can enter the gift in the regular gift module and track the proceeds the way you would have for an individual gift of securities. There is no functionality in regular FIMS that will handle 20 stocks any differently than 1. You will have to maintain the lots and accounting outside of FIMS.