In real life, every club pays in monthly installments, unless its someone like Real Madrid, Man City etc.
Just remember that 48 months is 4 years. And if you keep making big purchases every season, or even worst, every transfer window. You are likely to go the way of the pompey since your making too many monthly payments.
I tend to buy players only with immediate funds, unless he is arriving to my club at a future date or he is integral to my jigsaw puzzle and funds are low.