Interesting team overall. For Galvantula, it may be a good idea to replace thunder with thunderbolt. Thunderbolt is more accurate, and accuracy is important on bugs. On Ampharos, you might want to put an electric move on (such as thunder or thunderbolt) instead of heal bell. This way you have stab that will accompany it's heavy attack focus.
For Blissey, special attack is where you want to go, as her base special is 75, and base physical is only 10. The 4 attack EV's should go into special, and, honestly, power-up punch isn't the best option. However, the only special, normal-type moves it can learn (for stab) have sonewhat low base powers. Keeping calm mind on would boost these, and end up being stronger than p-up punch. Echoed voice is probably the best option here.
Aggron looks good. Haxorous looks good. I don't know how well substitute works, and with the speed and attack from dragon dance, it can work well by taking hits from pokes he doesn't OHKO, but with fairies running around, it might be better to put on poison jab. Lastly, Porygon-Z looks good too. I like the trick option to make you're opponent useless. One thing though, is it would give you more coverage to put on psychic instead of thunder, as Porygon-Z doesn't worry about water types too much. In addition, it would cover poison types, which could wear down Blissey and do decent damage, as well as cover Porygon-Z's weakness to fighting.
