Welcome, mister. Get ready for a life change!
You don't say whether you already have mods or know where to get them. One stop shopping:
http://web.mac.com/sixwilsons/OOTPMods/Main.html
There's naturally a reluctance to praise one member's work over another, so I will just inform you of the ones that I have used:
- Gambo's ballpark images and stadium data file.
- Uniform packs by Falcon, fhomess, and Matter 2003, and fictional stuff by silvam14.
- The facial hair mod by Bobble.
- Logos by just about everybody.
- Gambo's photo packs.
- The MLB 2007 roster by CubbyFan23 and haveband.
- Mood icons by Bobble.
Again, this is just what I have used in several leagues that I have created so far; there are tons of other mods that I never even tried! So, no nasty messages from folks whose wonderful work I have unintentionally ignored, please.
The best method is trial and experiment, saving games with different mods installed until you find an arrangement that you like. You will be one busy dude if you really get into modifying this already complicated and fascinating game, so consider yourself warned. Enjoy!