As for fonts, whether it be events or a welcome message, Blockland can use any font installed on your computer. If you use a font that is not installed on another person's computer, however, they will not be able to see it, and it will default to Times New Roman in their view.
But, on to the good stuff. To display a font, type the following:
<font:ExampleFont size:#>
For instance, you could replace "Example Font" with "Impact" (without the quotes, of course), and replace the "#" with "15". It would look like this:
<font:Impact size:15>
And you would see this:
This is an example.
Add some color to that, play around with the fonts, and you've got yourself a very nice-looking welcome message.