If you want a grafted avocado, buy one already grafted. That way, you can get exactly what you want. The avocado tree you grow from seed will not be like the avocado you ate to get the seed. If you did graft it, it would have to be the rootstock (as its a seed, grafting stock is taken from 'mother' trees), but, its not that easy. Rootstock is chosen for specific needs (soil type, weather, size, disease resistance...).
Yes, you can grow an avocado in a pot, but, no it won't have fruit. If you plant your avocado in the ground, it may have fruit eventually.
If you decide to grow an avocado tree, plant the pit in a 2-gallon pot (deeper than wide), in regular potting soil. Keep it watered. To keep it small enough for a pot, you will have to prune it. They make great houseplants with their big green leaves, but will need full sun to be healthy.