For now everybody's storage is 275 after last big upgrade but at some level I think isn't even enough, I'm level 94 with almost all the cars unlocked and need a lot of parts to upgrade them, 14 fuses and 15 clamps for example in koenisegg parts, so if you have for example 20 clamps and don't have cash to install them and you run out of space on your storage you really DON'T want to sell 5 clamps because are difficult to farm.
Some people said is better to focus in one car at a time but for me cannot do that, you cannot stop racing because you are not able to farm one car parts, you can start farming another cars parts too, so at some point like me right now, always my storage is full and is not enough to continue farming parts, really hurt me a lot when I need to sell some parts, for me fuses, relay and batteries are pure gold, my rates to pick up them is 1 after 6 chances, so if we do the maths when I need those 14 fuses I need to play around 84 races to get them, can play 18 fuses races per day, need around 5 days only to farm those fuses so when I'm run out of space on my storage make me fu.... angry.