I'm about 20 hours into my Japanese Pokemon Platinum rom. I just got the 7th badge. My current party is: Sceptile, Lv. 43; Typhlosion, Lv. 48; Marowak, Lv. 38; Dragonair, Lv. 39; plus a Staravia and Bibarel I keep to harbor 6 HM moves. I got the ones I use in battle as eggs from a friend at the beginning of the game. I've had to consult a guide at GameFAQs a couple of times when I didn't know where to go (the game has been changed pretty noticably since D/P, a lot more than Yellow, Crystal, or Emerald were from their respective generations. They even reordered a few of the gyms). I think it's pretty good, but I'm not sure if I'd buy it whenever the translation finishes.
EDIT: Wow there are a lot of opportunities to fight high-level trainers. There are trainers who go around Pokemon Centers that you can fight daily who have Pokemon in progressively increasing levels up to the mid-50's, there's a cafe you get access to after doing some sidequest where the trainers (gym leaders and people you've teamed up with) all have Pokemon in the 60's, and after getting the National Dex, I read the Elite Four is between levels 65 and 78 (though I haven't gotten past the third since getting the National Dex). Right now my team, consisting of the 4 I mentioned above, are all at level 70.