3 - I was playing with settings today and found the following:
In game go to video option then click the advanced tab
Set atos to all trees only (second last option)
Set object detail to low, this mostly affects grass and gave me about 10fps boost
Turn off post effects this also gives about a 10fps boost
If you do a search there are quite a lot of information on optimizing arma/day z but I found these made the biggest difference for me.
Also to view your frame rate in game you'll need a recording program like fraps or dxtory.