Hi @Andrea
SendGrid is a partner to Azure and for any technical queries related to send grid you need to contact the send grid support via https://support.sendgrid.com/
AFAIK there is no daily limit for free trier sendgrid account except the monthly limit as you have mentioned but this can be confirmed from the sendgrid support as they expose these limits.
To monitor the sendgrid you can click on manage and it will redirect you to sendgrid site where you can check the dashboard having different metrics. For more details on your queries, you can always reach out to sendgrid team.
Please 'Accept as answer' and ‘Upvote’ if it helped so that it can help others in the community looking for help on similar topics.