Flygon can be faster than houndoom, so unless you plan on hp ice on the switch(which wont happen a lot), it won´t get much use, between grass and electric, it all depends whether you want to hit gyarados or quagsire/swampert(even though both get crippled by wow)
For the evs, I would need to do calcs, while sp atk can increase your hp and fire stab moves, having crunch/pursuit or even low kick for the snorlax also looks good to me. For the item, Life ball would be the best but a scarf can surprise some things (Also with scarf, hp ice is not the worst idea)