Advice for postgame please?

[8bit_oj]

I just recently beat the Elite Four and Champion in Platinum, and I was wondering if it was common or a good idea to use a new team for the Post-Elite Four part of the game, like the Battle Frontier. I like a lot of Sinnoh Pokemon that I didn't use on my team up until now and thought it would be a good opportunity to use them.

Any advice on this or any other part of the Post-Elite Four part of Platinum (it's my first time getting so far, and I've been playing since Gold) would be great.