Your squad is slightly stronger, but you could buy a couple of 4* or low 5* I think. It depends on your server. You'll have to check his strikers' stats against your defenders, but you could also play a back four and zonal mark them.

The oldest I would buy is 30, if you buy a 31 year old, you might not be able to sell him before the end of the season, and then he might retire next season.