Don't pay an agency, whatever you do.
Build a website on something like wix / go daddy and make use of all the tools and guides, they're there to help you optimise as much as possible. Wherever there's an 'SEO' button, click it, and fill in all the page details. It makes a difference!
Utilising keywords is handy. You can get a keyword analysis on moz.com for free.
Link all your socials to the site and update regularly. If you can blog, that's ideal too.
Have a read up on YouTube optimisation if you're planning on making videos.
As mentioned, CANVA is a dream for graphics. If you upgrade to the pro version (£99 a year) you get access to all their images, and can white out backgrounds, which is really handy for product shots.
Facebook/Instagram advertising is easy, and very intuitive. Set your budget small and play with it. Make sure you fiddle with the audience reaches though, or you'll burn through £.
Go pro for Google ad words, they're a ballache. But stick with socials first, whilst you find your feet. Until your site is established and working for you re SEO, it's pointless wasting money there anyway.