Can I use fewer modules for implementing my newsletter?
I think that with 6000+ emails to send you need to use an external mailer like MailChip or MailUp. Remember that these services have the correct infrastructure to support massive send email and dashboard report.

We have written a module for 1 of our clients that permits to create NewsLetters in Drupal and send it via MailUP for example. 

However 7 modules to send an email are not a big number because in Drupal each module exec a single work:


Simplenews is the module that manages the newsletter (user subscribe,
unsubscribe, check, etc etc).
Mimemail, htmlmail and Mail system permits to create correct HTML
email and send it in correct way. And in this case you can reuse all
for the internal mail (wellcome, lost password, etc.).
Rules manage "the" rules of sending email (in this case).


In other systems you have a big module that manages all but not so good like single modules for single works. And in many cases the big module is not compatible with other modules. In Drupal I have found only very few cases where a module is not compatible with other modules.