Gyarados

No

The first is too low a starting point. The second isn't bad if you've got plenty of stardust - not the best move set, but useable.

You are better off spending dust on a Vaporeon, there isn't really a situation where you would want to use a gyarados instead

The Dragon Breath/Hydro pump is worth taking on as a long term project since the move set isn't available anymore (you can't just find/evolve another one). The bite/twister is a done deal. (I feel your pain as the owner of a 98% bite/twister myself.)

the first one is a lv 3 gyarados. it will take about 124k dust to get it to level 30. i don't think that's worth it just to be able to use dragon breath. it's not that special unless ur facing a lot of dragonites in ur area and u don't have a lapras / dewgong since bite will do the same dps ignoring type advantages.

if you like using gyarados and/or you have dust that you aren't using, don't let that stop you powering it up though.

i wouldn't power up a gyarados with twister, but keep both. dragon breath is no longer available so that gyarados does have value if/when trading comes out. you can still use the 1840 for battling, spamming bite still does a lot of damage, but imo it's not worth powering up any further.