If you put the base down before the resin has set, the resin will follow gravity to the bottom. The top Fountain styles are as varied as fountain designers. They can be as simple as a ceramic vase sitting in a ceramic bowl. You don't need to spend much, or anything to create a masterpiece. Take a fresh look at the stuff in your house and yard, especially junk you've been reluctant to throw out.
Waterproof adhesives are available at craft and hardware stores for bonding the elements.
Water conduit You will likely need some kind of conduit to get water from your pump to the top of your fountain. You want a tube or pipe that fits snugly onto the aperture of your pump. Vinyl tubing is flexible and can be worked into a small opening to create a snug fit. Acrylic pipe is stiff and clear. All work well, and in the amounts you will need, are fairly inexpensive.