In regards to ease of
GM'ing --- 40kRPGTools is brilliant for quick reference (
http://www.40krpgtools.com/), especially the armoury in my opinion.
Making quick reference sheets you believe you'll need is essential as well, one of the main detracting factors in a game is pausing in order to look up a rule/mechanism (if you find yourself without a quick reference sheet and need a ruling, use your best judgement and look it up later after the game).
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Now onto your main point. Instilling a sense of dread/horror/suspense in your players is HARD. No two-ways about it. Players are safe around a table, laughing, maybe enjoying a drink and able to look at phones/computer screens so how can you instill a sense of fear?
If you truly want to do a 'horror', you HAVE to control the environment. You want a quiet area with limited to no background noise, no lights apart from maybe a candle (best) or a low level lamp. Ban computers (use paper sheets) and limit phones to emergencies only. Once you set the mood your players will find it much easier to slip into the environments their characters exist in.
Then when you begin to do the game itself, less is more; throwing so much supernatural gak at them will desensitize them 'oh that's cool, is the shop open?'... you want them to imagine more than you ever show.
Here's a good link that helps with running horror
RPGs.
(
http://www.mindspring.com/~ernestm/horror/horror.html)