Write the revision policy before you write the price. At $600 a month and 9 hours you're at $67 an hour, and one client who treats captions as a draft process takes you to 14 hours without the fee changing. One round included, named hourly after, in the agreement.
Churn is the number that decides whether this is a business. Content clients leave heaviest in the first 90 days, and almost always because they expected listing appointments and got reach. Agree at signing what you're both looking at, profile visits and inbound DMs being the honest ones, and put it in the onboarding email so month three isn't a fight about attribution.
On the music point above, the exposure is worse than a wasted subscription. A track flagged for commercial use gets the audio stripped or the post pulled, and the strike lands on your client's account rather than yours. That is the phone call that ends a retainer.
Term and notice: a three month initial period with 30 days' written notice after that is normal and it stops February from being a surprise. Get paid on the first, not on delivery, or you'll be chasing $600 invoices for work already published.
And don't price as a share of anyone's commission. It makes every conversation an argument about which closing came from which reel, and depending on the state it can raise questions about whether you're being compensated for licensed activity. Confirm that with your state commission if anyone proposes it.