As Steve said above it might be worth us revisiting this to see if we can make any improvements but there is likely not much we can do. The problem comes in the way that WP identifies a requested page URL. Without the ‘/forum/’ page slug in place between the domain and the ‘/forum name/’ WP will identify the request as a page with that name – wont find it and will load the 404 template.It is the presence of the forum slug in the url that allows SP to ‘interfere’ in that process and redirect to a request to the forum.
As to the breadcrumbs question – as you are aware SP is now run completely by templates so to make this change you will need to edit the template which can be done in the SP theme editor panel. The template you need for this is the spHead.php template. Look for the call to the breadcrumbs display function which will probably look like this:
sp_BreadCrumbs('tagClass=spLeft spBreadCrumbs&tree=1', __sp('Home'));
If you want to just change the home link then you can add this to the arguments. For example:
sp_BreadCrumbs('tagClass=spLeft spBreadCrumbs&tree=1&homeLink=domain.com', __sp('Home'));
where domain.com is your link.
If you want to remove it completely then you will need to do the following:
sp_BreadCrumbs('tagClass=spLeft spBreadCrumbs&tree=1&homeLink=', __sp(''));
Note the ampersands and the use of case.
As always we recommend that you create your own SP theme so that any customisation is not lost during a future update. (http://codex.simple-press.com/codex/themes/theme-basics/creating-a-theme/)