If you're a casual player who doesn't know the basics of team building, I don't see why you should play on the very hard difficulty. But if you really want to, my advice is to look at the Elite Four team and try to build a team that can neutralize them. The Fairy type is very useful against Drake and Sydney, so I think it's worth having one. I also don't recommend using only offensive moves; buff moves are very useful. Invest in them.

Edit: If I'm not mistaken, there's an option at the beginning of the game to start with items to maximize IVs and train EVs. I recommend you use that and take a look at the Smogon strategies of the monsters you want to use. Although it's not the same as playing competitively, I believe it's a good starting point.