Hi, thanks for the response. I wasn't really clear about my thoughts behind the questions.
I was thinking of creating a blog website, and by itself it should be very fast because it won't need any special software, and very few plugins.
I was thinking to create the community website on a separate domain, because I want to keep the blog pages as fast as possible. The community plugin will have many more plugins and a lot of activity by members of the community, so I'm thinking that it would be quite slow.
If I add the community to the blog website, I think that the blog pages will load a lot more slowly. I would prefer to have the blog and the community on the same domain, but I don't want to sacrifice speed on the blog.
I've heard of a plugin called "Plugin Organizer" that I could use to stop the loading of plugins on particular pages. I have never used this so I don't know exactly how well it works, but apparently, if I keep the blog and community on the one domain, it could reduce the load on the blog pages by stopping the loading of community plugins, so that the pages remain fast-loading.
I think I remember reading that one of the JoomUnited products also does this (stop a page from loading plugins that it doesn't use). Is that right? If it does, I could keep the blog pages at lightening-fast speed while I have the slower community site in the same domain (in the same Wordpress installation).