It depends on your store type. If you're going for a niche store (like just selling sneakers or hoodies), 10-50 dropshipping products is a good start. Enough variety, but not too much to handle. If you want a general store (selling all kinds of stuff), you might need 50-100 dropshipping products to test what sells, but that takes more work.
I guess for general store you can have much more than just 100... There are many sellvia products packs that contain 500 or even 1000 items and the tend to be really profitable cuz every person who comes to your store will find something he likes. I like sellvia because of that, there's something for everyone
I make an one-product store, where I'm focus on just one hot dropshipping product and a couple of upsells. Another option is a small niche store with upsells – like 10-30 main products plus extras to boost sales.
Yeah it's actually a great tactics "Try and see", especially when it comes to choosing a dropshipping products. I did this when I was trying to figure out what will be selling best in my Sellvia store. In the end, I just stopped on one niche from Sellvia products packs that brought me the most of profits