So far my team consists of my two starters Chesnaught and Blastoise, Talonflame, Helioptile, and a Mismagius. The Chesnaught is a staller, using leech seed, toxic, defense buffs, and a rocky helmet to wear out foes. The Squirtle I got had an attack boosting nature, so I took him for a loop and made him a physical fighter. Talonflame Helioptile and Mismagius don't have much strategy in them yet, just generic moves. I'm on my way to the 8th gym from Anistar city. What pokemon could I get along the way? I prefer type diversity and a well rounded team, so based on my strategies, what could compliment the other 5?

I think a Ground type would work. Two of your Pokémon are weak to Electric and they are weak to Ground types. And with both Talonflame (a Flying type) and Mismagius (Levitate) in one team, you can still use Earthquake/Bulldoze sets in a Double or Triple battle. A good Ground type that you can catch late in the game is Piloswine. Piloswine is also an Ice type and has great stats overall as a Mamoswine.

I'd say go for something either steel or dragon with ground as a second type the first Pokémon that came to my mind when I read that was Aggron but you'd probably start with his first evolution Aron because not only would a steel type make a great addition and help cover potential weaknesses Aggron has an amazing defense stat like all steel but is also a ground type covering even more weakness and giving you access to moves like S.T.A.B. (same, type, attack, bonus) Earthquake and Rock Slide but Aggron can Mega evolve to become even stronger. Another Pokémon that would go really good on your team would be Flygon or start off with his first form Trapinch, Flygon is a good choice because its Ground, Dragon typing we've already covered why you'd want a ground type and you'd like a dragon type because dragons aren't weak to very many types and are strong against most types having a dragon type also gives you access to my favorite move Draco Meteor. Anyway those are my suggestions hope this helps. 

Honestly, Going with a Goodra would be a smare choice. It can use a good variety of special and physical attacks, and it's special defense stat is the best among gen 6 pokemon. Those are good reasons to make Goodra be your 6th pokemon.

I'm sorry for taking so long to reply, but I did check this thread out offline 2 days ago, and I decided a good pokemon to mess around with was Mamoswine! I really do like your ideas for double teams, and since Helioptile has sand stream I can use sandstorm as well! I also like using ice moves, even if frozen conditions don't even last a whole turn. XD Thanks for the suggestions guys!

Looks like the only decent thing on rout 17 is Abomasnow. An ice type could compliment what you've got and help with the dragon lady in the championship.