If you are thinking of hiring an Inbound marketing agency, or recruiting an in-house team, audit the skills you already have then find an agency that can work in partnership with your team to get the best possible outcome.

You'll need a range of skills including
strategy
planning
design
web development
SEO
content creation
social media

An agency can be much more cost-effective as you are only using a proportion of their team's time rather than 100% of an in-house team.