Build the spine first, then improve one weak role
Start with goal protection, ball recovery, chance creation, and finishing. Keep the chemistry connections that make those roles work together, and avoid replacing several cards at once.
A squad can look stronger on individual cards and still perform worse as a team. The safest build process is to identify the weakest job, test one replacement, and compare the result in the same mode. This makes it easier to tell whether chemistry, role coverage, or the card itself caused the change.