I see two main approaches to consider:
1) is the Hubspot Product-Market and Model-Channel approach or Growth framework. It is good if you don't know your final product and you do marketing at the same time with development. Here is a big post.
2) Another approach is named as growthhacking or Bullseye framework. It is good for services which have already stable product. You think about channels, select best, test, and double / triple in case of success. You can google for more details. Do not find best link now.
Great content, also called ever green content is never obsolete. It can work for you for ever.
Creating authority and building your SEO takes time. I recommend you start ASAP.
I use ahrefs for connecting with influencers (search backlinks of your competitors), researching keywords and more. You can see some of the top ranking articles are a few years old.
Here is my research on marketing. You can find lots of great articles on growth hacking.
For networking work in shared space offices and lot of networking meetings.
Write How To blog posts. Curate and use your curated articles to build sky scraper type blogs. Here is our chrome extension called kurator.
I would recommend you create your own content (I'm assuming you're referring to imagery? Copywriting?) only if those are skills you truly possess (be honest with yourself). I've met with too many entrepreneurs that are brilliant product developers that simply don't have an eye for outstanding branding, nor the writing skills for adequate blog posts. That said, "create your own" or "hire a company" are not the only options. There's a middle ground. If you don't have a budget to hire an agency, you may outsource a single individual to take care of these things for you.