Can I sell on my shop other products than those created with T-Pop?

Of couse! It will not cause any problems.
If you decide to sell products that you did not create using T-Pop, nothing is to be expected, it will work automatically.

If an order contains a product created through our app and a product from another platform, we will only receive the product synchronized with T-Pop and we will fulfill only the part that concerns us (and we'll add the tracking number, if applicable).