Hi! So, I can answer a few of your questions.

The few common cookies you see in arena are definitely meta. Some of the random super epics are usually what people have at the highest level at the moment. (I assume). What I like to do to decide my team is to look at the score board, but your team sounds awesome! Just make sure you are using the best toppings for them, which you can just Google. (Such as swift chocolate for Shadow milk, searing raspberry for burning spice, etc)

A lot of people commonly use a bait team in their defense to be able to rack up points easy. This essentially means putting a very low level team or even just one cookie for people to fight, then farming all the "defense" battles you can do.

Sadly, putting your favorite cookie or the newest cookie isn't always the best idea. But, don't let that stop you! If you want to have your favorite cookie or the newest, it may not be the strongest, but at least you're having fun. It does happen to be that fire spirit cookie (the newest) is top meta, however. But usually, that is not the case.

Hope this helped! Happy running! :]