About 4 years ago my neighbour at the allotment gave me a couple of cape gooseberry plants in june/july. They were about 3" tall .. I just dug a small hole and planted the contents from the "3 pot into it (outside). They grew into bushes about 24" tall.
The following year I saved a few of gooseberries and used the seed to grow my own .. about 10 bushes ! .. I'm afraid most people thing of them as a treat or delicacy, but you can only eat so many of them and I haven't bothered since.
Pot them on when they are big enough to handle .. harden them off .. and plant out when the risk of frost has well and truly gone.
If you do grow them create a low windbreak as they were easily damaged.
I don't know how they count the seeds when you buy them .. they are like dust ? But if you save just one gooseberry it will give you thousands of seeds.