There's car guys with guns and gun guys with cars. I was a gun guy before a car guy. To answer the OP's original question the best place in a car to have a pistol or revolver is where you feel most comfortable with it. It's a personal decision and asking that question on an internet forum has...
You should have upgraded the intercooler first. The catback and CAI are shiny things that sound cool that will not increase any performance in you car. In fact depending on the CAI you install it may lower your HP/TQ. It's been proven that a stock box with a drop in filter is the best mod for...
We have discussed OEM air box vrs. CAI here extensively and the proven conclusion (before and after on a chassis dyno) is the stock box is an excellent design and with a drop-in filter such as a AEM or KnN provides a incremental increase in HP/TQ and the CAI while looking cool and having "noise"...
Make sure battery is at full charge (12.8v) and disconnect the negative battery cable and call it good. I leave my Mustang in the summer this way while I travel for 10 to 12 weeks.
The OEM strut/shocks will not support the spring rate of the Proline springs. It makes sense total sense to change the strut/shocks since you are right there doing that spring work anyway.
If you go with the Sportlines be aware that you be changing the geometry of the suspension which will need to be corrected. You will also need the Steeda Bump Steer kit which will be adjusted during your four wheel alignment. The only other thing I can add is with those springs you may not want...
I think it's at the point where the OP feels if he asks enough questions he'll finally get the answer he wants to hear. Unfortunately for him not on this forum.
It depends on what you're going to do with your car but since you're changing springs might as well upgrade the struts and shocks while you're right there.
I saw you post on the other forum but I'll reply here. If you are making 23 lbs. of boost I doubt you have a boost leak. Perhaps there is an issue with the BOV. An intercooler is a dumb system, no moving parts just a heat exchanger. Make sure all your pipe to hose connections are good, clamps...