Hi!
I believe there is nothing wrong with your methods. However, it is better to send an offer if the brief has everything you need to understand the amount of work you will be doing.
Similarly, in most cases, it is better to send a message and ask them to discuss it further. (it has worked for me in most cases)
Here is an example of how I would handle a brief/opportunity
BUYER - I need ten SEO blog posts on a monthly basis for my new gardening blog. BUDGET - 100 USD
MY RESPONSE - Greetings! I understand you are looking for a writer with expertise in SEO. I have been doing it since 2018, and so far, I have only exceeded the expectations of my clients. I would send the offer, but I need to clarify certain details. Please let me know when you are available to talk. Best Regards!
Finally, try to keep your message short and to the point. In my experience, most buyers may not have time to go through a message of more than 150 words.
I hope it helps!