Answers

Surround sound is generally installed in front of and around an entertainment system including your TV or video monitor and often several locations throughout the house may need surround sound as in Home Theaters.  It should just be a few hundred dollars per system, per location to prewire surround.  If you are looking for whole house sound systems, that is a different story and generally each room is not surround but has stereo speakers and depending on the number of rooms and your distribution system, it can vary quite a bit.  Most good security systems today are wireless and I would highly recommend any glass door or window area easily accessible from the outside have glass breakage sensors.

I am assuming it is a standard steel entry door handset.  If the screws are not striped, simply tighten the screws as you would on any entry or passage set.

I probably would not recomend it.  A laminate floor is a floating floor and the flex, expansion and contraction of both as well as the hollow sound you can have with a laminate may give you undesireable results.  Laminates come out very easily and I feel it worth your while to remove the 1st laminate to elimate any future floor structural issues and install the new floor to the manufacturer's specifications.