Statues (at least in my experimentation of building a fish farm) have a hard delay of about half a second before they spawn another monster, in addition to a limit on the number of alive monsters spawned at once (which is 3, if I remember correctly).
The optimal spawn setup seems to honestly just use a timer (one second, of course) hooked up to part of the statue, then a series of pressure plates near an area enemies are going to walk on. Reason being, their motion will try to trigger the spawn again instantly. This works especially well if you have it hooked up to a dart trap, as enemies will often jump at walls and retrigger the buttons repeatedly as long as they're trying to get at you, sending darts out all the time.
In my experimentation having more than two input lines in this setup doesn't change a whole lot in terms of rate of action.
One thing to remember is that wires in Terraria are not like Minecraft -- they do not have "on" and "off" states. They simply "pulse". So while a lever may look like it changes states, every time you click on it, it pulses a signal again.
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I will say, though, that I haven't experimented with multiple one-second timers. I don't think it'd do much other than provide a more reliable rate (if you can even get them desynced in the first place)...
I have put enemies under specific lists based on how they pose a threat to your property.
Enemies of Property
Can hit through Walls
Damage Property
Can enter home without doors
Goblin Sorcerer
Vampires
Wraiths
Threats based on Time
Threats during Night
During Moons
Werewolves (Full Moon)
Clown (Blood Moon)
Solar Eclipses
The following are strategies from the wiki I have put what threats will remain after you have completed the follow concepts.
Strategies
Digging a Deep Pit
Threats Left: Sorcerer, Demon Eye, Worms
A simple defense would be to dig a ditch underground that is too deep to jump out of, yet retains a way for a player to escape. A simple ditch would be dug out more than six blocks down, four blocks wide, with a ceiling of no more than four blocks high, while leaving a small area on the side of the pit opposite of your door so a player can jump up. If this is built properly, the only monsters capable of entering a house are the Sorcerer and the Demon Eye (most Goblins cannot enter because nobody can jump far enough with such a low ceiling). To remedy the Demon Eye problem, simply put a door on the other side of the ditch, as demonstrated on the left. Furthermore, if you dig a little farther until the Zombies can walk off screen, they will automatically despawn after enough time of being off screen, so the player doesn't have to worry about risking their life to kill a horde of Zombies.
Suspension House
Threats left: Flying Monsters, Sorcerer, Worms, Bosses
To counter flying monsters its recommended to use platform traps and doors.
Building a house in the air prevents any sort of land monster from entering the house regardless of their ability to knock down doors. Flying creatures can still be a problem but are easily nullified with platform traps and doors. Building a house like this is completely impenetrable except by Sorcerer, Worms, or bosses. As seen in the screenshot on the right, only one Zombie is allowed to spawn despite Blood Moon due to how many Demon Eyes are trapped. In addition, the player can fight on the ground with melee or from the central "airlock" of the house with ranged weapons. The only issue with this type of house is it can be detrimental to one's sense of gravity.
Advanced Approach
Threats Left: Demon Eyes
The major defense against basically all enemies is to have some type of block that stands out from all the others, and put it above the doors, then put at least three blocks of sand above it. One can now leave the door open almost 95% of time. Make sure that the door is opposite of where the sand is, otherwise the sand will just land on the door and sit there.
Sources
http://terraria.wikia.com/wiki/House_Defense
Best Answer
Recipe for key mold farm:
Use you rolling pin until you make sure that you got a really good flatten surface.
Spread Crimson all over the place.
Get 200ml of Battle Potion and a Water Candle.
Put some Jungle Temple traps to your taste. Dart and Spike Balls prefered.
Make a cool wall to avoid the jumping enemies going to where you are and not being hit by your own traps.
You can repeat the process to have 2 floor of enemies walking to their deaths.
Note: Make sure that you have no holes/caves beneath you, otherwise some mobs spawns will be lost, just because there's a stupid mob where you can't see.