Thought you were nuts when I saw your drawings. Only realised what was going on when I replied and saw them as a quote
As Andy said, non-visible surfaces are ignored, so I don't think the top one would be any more efficient (maybe quicker to compile). BTW, the top one is concave and therefore invalid as one brush anyway.
More lights definately slow down compile, but I don't think they matter in-game. Models... well, they are lit 'more dynamically' than the rest of the map, but whether lighting them is significantly more work for the computer is doubtful. Their lighting will be simplified.
For the hole:
1) Make the hole in a block that it just the right size, then build the rest of the wall around that.
2) Vertex manip. is best
3) You could divide the block into smaller blocks, and then VM the verticies in the middle. Pull them outwards.
So here's a drawing from the front. You'll need to click reply to this message, then click the quote button to see it correctly.
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| |__/ __| |
| |_| |_| |
| |____/__| |
The VM tuts here at TWHL might help.
Getting more points can be done by splitting faces. In VM mode, select two vertices or two edges and press Ctrl+F. I think its mensioned in the first VM tut. BUT, doing this is perhaps the easiest way to get invalid solids. Rather just use more blocks.