You can make any team have full stats by editing each players stats and 
upgrading them to 99. However, be warned; if you start with this team in manager 
mode, your salary will be high. Make sure to cut their contracts down as soon as 
possible.

To start with a five star team immediately in career mode, go to the team 
management screen. Put the bad players in the first eleven so that your team 
will be a four star team. Then go to career mode. Your team should be there. 
Save your career, then go back to the team management screen. Put the first 
eleven players back, save it, and you will have the normal team on friendlies 
and your team on career mode.

Use the following trick to be any team desired in career mode without buying 
better career teams from the fan shop. First, go to team management and choose a 
four and a half or five star team. Put all their worst players into the starting 
line up. They need to go down to about four stars or less. You can then use them 
in career mode. When you have begun your career you can change your team back.