1. I would like to know which plan I should subscribe to if I want to be able to put my company email address when sending email.

2. Also we have dkim / dmarc activated. Is this likely to be a problem or you have a workaround?

You better contact the support of LimeSurvey GmbH directly (see Support on this website). If you use the email-server of LimeSurvey GmbH, you will need to know which IPs are used and can ask the admins inside your company to update DKIM / DMARC to ensure that LimeSurvey is allowed to send E-mails with your company domain.

I would recommend to use a special emailaccount of your company for surveys. You can let LimeSurvey send the emails over that emailaccount. That is easier to implement.