Cold outreach help

We recently started a small post-production studio and are trying cold email for outreach.

Current setup: • 1 domain • 1 mailbox • sending ~15 emails/day • using Apollo for leads and Instantly for sending

A few questions:

1. Is 15 emails/day too low? What should we realistically aim for with one mailbox?
2. When should we start adding more domains or inboxes?
3. Are Apollo + Instantly still a good stack, or are there better / cheaper alternatives?

Since we’re just starting out, we're trying to keep costs low but still do things the right way.

Would love to hear what tools and sending volumes others are using.