Hi guys,
Answering your questions:
1. MailPoet won't work with SMTP plugins, simple because we don't use the wp_mail() function to send emails. Our PHPMailer library is heavily modified, this is one of the reasons we can't use wp_mail(). Yes, there's a trick to use it, and it might work, but we can't provide support for you if you use this trick and it doesn't work, okay? This is not "us" being presumptuous, just careful.
2. We recommend SendGrid because we have built-in support for their API. The same for ElasticEmail.
3. Yes, you can select your from address, it's on Step 3 of the newsletter creation process.
Cool?