How to start SEO for an old website?

I have worked on similar aged e-commerce sites and faced the same situation. From what you’ve shared, your foundation looks solid especially the consistent blog updates and internal linking. In my experience, backlink velocity matters, but relevance and quality make the biggest difference. Instead of bulk buying, I’ve focused on gradually earning links from niche-relevant sources and UK-based content when the target market is UK. That geo-relevance often improves local visibility

Your SEO efforts are solid, especially with content and on-page optimizations. Regarding backlinks:

1. Quantity isn’t everything—quality matters more. Buying backlinks in bulk is risky and can hurt your rankings if they’re low-quality or spammy.
2. Focus on earning high-quality, relevant backlinks from reputable sites, ideally related to your niche and UK-based since your market is the UK.
3. The number of backlinks needed varies, but consistent, natural link building (like your 2 guest posts per week) is better than large spikes.
4. Keep monitoring your backlink profile and focus on relevance and authority over volume.

First thing I’d do is run a full audit, check what’s indexed, spot technical issues, and see what’s already ranking (even if low). Then update outdated pages, fix internal linking, and slowly build topical clusters. Start clean, not fast