How can I transfer my data from Aweber to GetResponse and clean up my contact list?

Do you think that I will be safe from being flagged by GetResponse if I clean my old list of 2,500 double opt-in subscribers for dead email addresses and provide a clear unsubscribe link in my reintroduction message before importing it? Are there any restrictions or problems I should be aware of before uploading the cleaned list to GetResponse? What email cleaning service do you recommend as the best value?