Most cost effective smokes & other detectors for Elk M1

Greetings,
 
Getting ready to install an Elk M1 Gold for the first time at my house.
 
Going to try and run wires for as many components as possible.
 
Upstairs we have 3 bedrooms.  Right now these bedrooms and the hallway each have a battery operated smoke detector.  I wanted to add low voltage smokes as well (my understanding is that I still need the battery operated ones?).  What are the most cost effective smokes that I can install here?  Do I just need to run a single 4 conductor up from my basement where the panel will be installed, to my attic which is where I will access the ceilings for these bedrooms?
 
Same question as above but for Carbon monoxide and propane gas.  I have a coal stove, and some propane appliances operating in the house and would like to string a few of these monitors around where possible.
 
I haven't decided if I'm going to do wireless yet or not.  But it looks like there are 3 different directions to go as far as wireless with the Elk?  What probably makes the most sense to me would be to get the ELK-M1GSYS4STW which includes a 2-way wireless transceiver.  However, I see that I could alternatively buy a GE or Honeywell wireless transceiver?  Is there any consensus on overall cost effectiveness vs flexibility of options available going one direction over the other?
 
Thank you

I would recommend wiring the smoke detectors as a true daisy chain, with one cable from the panel to the first smoke, and then on to the next, and so on.
 
2-wire smokes are simpler to wire - no end of line power supervision relays are required.  But you need to use smoke detectors that are certified for use with the Elk.  Compatible 2-wire smokes are listed in the M1 manual and/or on the manufacturers' web site.
 
Something to consider is a combination smoke/CO detector, like the System Sensor i4 series.  You may still want to have separate CO-only or propane detectors in some places.
 
Whether or not you will still need your standalone smoke alarms depends on the local building codes and your AHJ.
 
Wireless detectors will cost you significantly more than hard wired.  If you have the ability to run cables, that's what I would choose.  Since this is life safety equipment, I prefer wired over wireless.  Just that much less that can go wrong.
 
@sandpiper just posted a nice FAQ on smoke detectors that you may find helpful.