First of all it depends on the scope of the project. If you want to build a CMS to suit your specific niche needs, then it is a good idea. But if you want to launch a CMS as a product to compete other CMS in the market then you need a feasibility / reality check. So first clarify this in your question. To launch your own CMS, you need to describe your Website / Business needs, so that I can suggest you better.

I have seen many startups and projects rise and vanish, in short period of time. The only ones that stay and gain true momentum are original in essence and provide value to users. If you truly want to carry on this platform and make it a renowned destination for fun, you need to shift your focus from revenues to value proposition, in long run. To simply put, you need to think and brainstorm, how you can more useful or beneficial for your current users ? If you can add value consistently, while maintaining your costs, your returns will be far better.

Hi, for all general purpose SEO requirements, Yoast SEO plugin is the best. With zero compatibility issues. https://wordpress.org/plugins/wordpress-seo/ If you have any specific requirements or problems, kindly ask again and I will be happy to answer.