What do I need from SEO?

So I have an okay knowledge of seo and have gotten my business to the top 1-3 in all our key search terms. I have used on site and a silo based system to get us there. I also invested in digital pr to get da 80-90 sites to link to us and have improved our domain authority on ahrefs from 12 to 33. i feel we are in a good position to attack the top spot in each key term. However, i have reached my time capacity and knowledge to get us there. This is non local seo. My issue with outsourcing this is that i already know quite a bit of SEO such as onsite and content optimisation. I therefpre need to find an SEO who can take us over the line to top 1. 1. What should i be looking for ? Monthly retainers or one of work based on keywords? 2. How much should i realisticslly be paying 3. How do i know the seo engage is any good? Its so easy for them to say it takes 12 months with no actual results