My recommendation would be to re-optimise the same page to a new product name (title/H1...etc) if the users expect that product name. If it's still an unknown term then ensure that you have the new name present on the site in form of a disclosure: e.g. This product is now officially called XYZ and that will ensure you're found for it. The only thing you're missing out on is phrase in URL. Potentially when consumers do the switch of terminology you could set up a new URL and 301 the old one to it.

Agreed, community is something that can not only educate but get you going and inspire to do more and better. It does get a bit lonely if you are hiding under a rock for too long.

Having a TLD specific to a country/region makes sense not only from SEO but also business point of view. I understand what it means to start again and building links again from scratch however you have a good headstart and a super relevant link from your old juiced up site. Google will figure it out it's the same brand, country specific and will start treating it as a family of websites. Make sure you use all local signals (phone, address, business reg numbers and are present in local directories). When interlinking own sites ensure good disclosure is in place.

Consider how your related articles are handled. At the end of an article you could have related content which is great for both search engines and readers.

I'm also curious to hear why change to Joomla? I find WP to be a superior solution in many ways although not as robust as drupal and others. The support network for it is amazing and the number of plugins available for it outweight many limitations it may have as a platform.