Lets get to the point.
My team that I find to be good for getting through the game with is...
Torterra: Torterra is a great physically offensive and defensive grass choice for this and the only thing you will really have to worry about with this Pokemon is an Ice type or the ice gym in general.
I'd use leftovers with this set. Torterra you can get as your starter if you choose Turtwig, Turtwig will evolve into grovel at level 18, then to Torterra at level 32.
Moves: Earthquake, Wood Hammer, Stone Edge, Synthesis/ Leech seed.
Since Ice is a problem, that leads me too...
Houndoom: Houndoom (If you didn't choose Infernape) is in my opinion the best Fire type in the game. What it may lack in defense, it makes up for in Special Attack. Houndoom is a great counter to many threats as long as it goes first which is why I recommend maybe a timid nature. I don't have a preferred item. You can catch a Houndour at route 214, and valor lakefront and it will evolve at level 24 into houndoom.
Moves: Flamethrower, Dark Pulse, Will-O-Wisp (or any filler), Nasty Plot
Well we need someone for Surfing so lets use...
Gastrodon: I chose Gastrodon as my water type/ surfer rather than the popular choice of Floatzel because in my opinion, Floatzel is kinda like a piece of paper. It can still hurt a lot ( paper cuts) but it can be easily destroyed. as we move on in my list, I don't really have a main wall Pokemon besides torterra, so I need someone with some defense. As Gastrodon isn't very powerful, he can definitely get the task at hand accomplished. Quick claw may be useful for an item, and maybe a modest nature. You can catch a Gastrodon at any of these places. Route 205, 212, 213, 218, 224, Canalave City, Fuego Ironworks, Pastoria City, and the Valley Windworks.
Moves: Surf, Earth Power, Recover, Ice beam (or another HM, but the rest of the HM's Gastrodon learns are physical.)
Well I guess we need someone with fly now don't we?
Togekiss: I chose Togekiss rather than the popular choice of Staraptor because all staraptor has more of than togekiss is attack and speed. Togekiss has the same base HP, levels up faster, is more defensive, and personally I like special attackers so togekiss is a no brainer for me. Yes Fly is physical, but its not meant for battle. maybe a timid or modest nature would work ( at least for me) and item is your choice. You can get a togepi egg in eterna city from cynthia. to evolve togepi, you must level it up at maximum happiness, which will get you a togetic, then use a shiny stone to get a togekiss.
Moves: Fly, Aura Sphere, Air slash, Flamethrower/ Wish (or any filler move really)
Lets try a good all around Pokemon now shall we?
Lucario: I chose Lucario as a filler Pokemon because Lucario is an amazing all around Pokemon for multiple purposes. his attack and special attack are almost identical (110 attack and 115 sp attack) so you could go either way. I prefer special, but ill put a physical set here too. As for the item maybe an expert belt, and nature is your choice. You can get a riolu egg from riley at iron island. To evolve roil, you must level him up at max happiness in the daytime.
Moves for a special set: Aura Sphere, Dragon Pulse, Flash cannon, Psychic ( any filler)
Moves for a physical set: Strength, Extreme Speed, Close Combat, I recommend Drain punch but whatever you want here is fine.
Lastly but not least, another all around beast...
Electivire: I chose elective for many reasons. While a popular choice may be Luxray, and I have nothing against Luxray, I find elective to be a better choice because of the move set, as well as the base stats (Which are only a little better which is why luxray is fine too) and electivire levels up faster than luxray. I prefer an air balloon for an item and an adamant nature for electivire.
you won't be able to obtain this Pokemon until later in the game ,(use luxray until then) but when you get to route 222, you can find electabuzz to catch. Once you have one, you must trade it to a friend who has a copy of the game while electabuzz is holding the electrizer. To get the Electrizer, you must surf behind the valley wind works to find it. I would put Garchomp here, but that I thought would be too many Ground types. I am totally ok if you use garchomp, but thats too many ground types for me. Garchomp could also replace Lucario too, if you wanted to.
Moves: Ice Punch, Thunder Punch, Earthquake, Brick Break.
Moves if you HAAAD to do Luxray: Crunch, Spark, Ice Fang (EGG MOVE), and superpower.
Moves if you did choose Garchomp: Earthquake, Dragon claw, Brick Break, Swords Dance
I hope this was detailed enough and I hoped it helped you on your platinum team!