I use a lot of data myself.

You are very correct to use the match ratings. There are dud signings and surprise signings just like in real life. You need to be careful not to be too hasty as it can take a player a while to get to good form with you but if it Drags on you have to cut your losses. Don't be afraid to play a lower rated player who produces for you either. My leader in goals produced is the lowest rated starter on my team. I just can't take him out when he is producing more than a goal a game and getting MoM every 3-4 games.

I have a CDM that was a high 6* and played poorly for the first 10 or so matches but right when I was about to give up he had 2 straight 8 ratings and scored twice. He hasn't had a rating under 7 since.