wrathofmobius wrote:
Is it possible to merge multiple brushes into one?

Not really.

wrathofmobius wrote:
... the huge amount of brushes makes ~5600 visleaves

This isn't quite accurate. As long as they make a flat surface, more brushes will not cut up the visleaves. Allow me to demonstrate with an example:

https://dl.dropbox.com/u/19093054/visleaf.png

Note that while the wall is made up of 32 brushes, they do not dissect the visleaf (the edges of which are highlighted in blue). If the brushes make a flat surface, meging them into one will not change the visleaf layout.

And as Nacimota pointed out: they don't cut corners visleaves. The different blocks can very well be used to add some texture variation to the walls. Something like this:

Brainstone wrote:
However, visleaf are split automatically, every 512 units. (Or was it 1024, I don't quite remember)

Every 1024th from the map origin, along all three axes (these points are marked with orange/brown lines in Hammer).

wrathofmobius wrote:
Thanks for the informative replies. What can I do to get my visleaf count down? Or is ~5600 acceptable?

Depends on the size of your map.
The most efficient way to get your number of visleaves down is to use func_details.

look normal
don't split visleaves
don't seal your map
can't be dynamic

use this on all things that don't block the player's line of sight like:
* angled pannels
* Tiles on the floor and/or on the ceiling where the ceiling isn't completely blocking the line of sight in destroyed theme.
* Other things that don't block the players Line of sight.

Just look at Valve's light instances which you can pop in walls. They have a hint brush over it so then the vis leaf won't be cut in some odd way.