Hi
Thanks for planning on using 4SEO.
As sh404SEF was doing both meta and OpenGraph, there is a direct and automated migration path from sh404SEF to 4SEF (for SEF URLs) and 4SEO (all the rest and much more).
But indeed there's nothing to import your data from OSMeta or ochOpenGraph, and you need to be aware of that and decide on how you want to handle data transfer. I don't know how much data you have in either extensions, so maybe that's not really an issue but you do mention "a lot of content" so it may be one as well.
on a test copy of TallAndTrue.com first?
100%. You can't do such important changes to your site on the live version.
However, will it simply be a case of uninstalling the OSMeta Pro and ochOpenGraph and installing 4SEO, or should I allow more time for the install and configuration?
You need time. SEO is not a matter of "install an extension and be done with it". You need to decide what you want to do, which features to enable or not, etc
4SEO works very, very differently from any other (SEO) extension. It does work just like Google, it's a crawler that will analyze all pages on your site, and then will keep "watching" the site for changes. Note that while you do that on the test copy first, you'll redo it when you go live.
While the initial analysis can last a long time, hours or more, other functions of 4SEO do work in the mean time (structured data generation, opengraph/twitter card, any redirection, meta data rule, ...). 1st version of sitemap and auto-canonical are generated only after the full first analysis has completed. Updates are done in the background.
Please have a look at the documentation. It'll give you a good view of how this all work.
I've got a lot of content on my website, and I feel it's not showing up properly in search results.
Just be aware that 4SEO will do the 95% of what can be automated, and give you the tools to do the rest, today's SEO really is about your content. Not it's items count, but it's value (in the eyes of search engines). There's no magic wand, although the sort of things 4SEO do is the mandatory basic things, required to just be in the race.
Best regards,
Yannick Gaultier