If you just want the "hot" experience without the installation headache, look for a save that says "Start of Game - Max Credits + All DLC." This lets you play the campaign from the beginning in a 2012 Audi R8, rather than loading a save that has already finished every race.
You can find pre-completed save files on community forums like Xpgamesaves The "Rehash and Resign" Step: forza horizon 1 save game hot