If you couple it with a Hippowdon with Sand Stream and a Smooth Rock, then definitely the Sand Rush ability would be best since with it you would pretty much outspeed everything in the game and if you get a SD up you pretty much sweep everything. However, if don't plan on using sand than go with Mold Breaker to hit those Levitate users. I'd recommend always a SD set with Rock Slide, EQ, and Iron Head.
I suggest you look in this thread. It lists the availability of all pokemons of a certain type before each gym. In the case of Florinia, there's Woobat, Ducklett, Wingull and many others, just choose whichever mon you think fits best in your team.
A great tanky pokemon that could replace the Meowstic is Reuniclus, especially if you give it Calm Mind. Also, don't see much of a point on having Tynamo since Greninja covers water pretty well. Try another Ground type, I'd recommend Mamoswine.
EDIT:
Those gen V pokemon always confuse me... Magnezone is a much better electric type, and it is pretty tanky as well.
Between the two the Weather Trio is more fitting imo, but I think it should be used when we encounter the legendaries.
I personally think that the Sky Peak Final Pass remix would fit quite well as Lin's theme:
https://www.youtube.com/watch?v=BqCJfwyMxZM&index=31&list=PL9793A30C55CED7F6