Calculating template page numbers
Your method names do not follow capitalization standards, they should be PascalCase. 

However, what's worse is that their names do not correspond to that they do: 


displayTemplateNumbers() returns a formatted string (and thus doesn't "display" anything), 
totalAmountOfDeletedTags() feels like it should be a property instead of a method.


And totalAmountOfDeletedTags() isn't even necessary, since it can be replaced by simple LINQ: _currentTagCollection.Count(x =&gt; x.Deleted);. And since you only need the active tags, you can simply do var activeTags = _currentTagCollection.Count(x =&gt; !x.Deleted); (h/t to @RobertSnyder).



At the end of displayTemplateNumbers() you twice call string.Format(). Instead you should do this once:

return string.Format("{0} products, {1} page{2}", 
    activeTags / _selectedTemplateConfiguration.TemplateConfigurationTagsPerRow, 
    totalPagesActive,
    (totalPagesActive &gt; 1 ? "s" : string.Empty));