Hi Alex,

I would try to answer some of your questions that you have,

For the question about - having a page for people going to urls which do not exist: http://mywebsite/urlwhichdoesnotexist could load a page previously designed informing our users that there is nothing there. You could make a 404 document type, and create a 404 page in your Umbraco installation.

When you have done this then you can refers the the id of the page, in the umbracoSettings.config, when the user enter a URL that not exsist then he will see the 404 page. Try to see this documentation on how to add the id of the page, in the umbracoSettings.config https://our.umbraco.org/documentation/Using-Umbraco/Config-files/umbracoSettings/#Errors. You can find the umbracoSettings.config in your Umbraco installation file structure \Config.

Have a Field as part of a document type for quick redirection. I would like to be able to have a page A on which I can say redirect pages B,C,D so that when a user tries to reach B, C, or D, they are redirected to A.

For the question on how to easy redirect page B, C, or D to page A you could use the build in propertyAlias called umbracoRedirect https://our.umbraco.org/wiki/reference/umbraco-best-practices/umbracoredirect another option could be using the umbracoInternalRedirectId https://our.umbraco.org/wiki/reference/umbraco-best-practices/umbracointernalredirectid

If you are looking for a package to make redirects, I would recommed you to take a look at the 301 URL tracker with this package you can manage URLs within umbraco. It automatically tracks URL changes if you for instance when a node is renamed, and makes sure the old URL will redirect to the new location. And you can also create your own redirects, based on a simple URL or using a Regex pattern. You can redirect to an existing node or a manually entered URL. https://our.umbraco.org/projects/developer-tools/301-url-tracker

Hope this helps,

/Dennis