Hello C0coontech Nation,
I've been searching the forum over the last few weeks and been researching which components I need for my Elk M1 install.  After searching I need a sanity check as well as a couple questions answered before I order parts.
My system wants are as follows:
1. Alarm with wireless sensors (Home is from the 70's and not pre wired). Thinking Honewell wireless adapter.
2. Keypads, 2 KPB's and a KPAS. Do I still need an extra speaker for voice with KPB's? If so, am I better off buying the KP2's since a speaker can be located behind them?
3. For lighting control I plan to use UPB so I'm planning on the ELKPCSPIM module
4. I'd like to control my landscape lighting and irrigation. (8 zones for irrigation and no more than 8 zone for lighting). M1XOVR or M1RB?
5. Would like internet alarm monitoring with cell back up.  I'm certain I need the M1XEP module but i'm a little fuzzy on what to use for a cellular backup. No LAN line.
6. Can you buy a M1 starter kit with a KPB or do they only offer a KP in the kit?
7. I used the current calculator and I was around 1.6 amps with all the components. Do I get another TRG1640 that comes with the kits or is there another option?
8. As for battery backup I'd like to have 8 hours worth. Do the larger batteries all fit on the same mounting shelf?
9. I'm planning on a 28" can just to be sure.
I know this is a long post but your help is greatly appreciated. There are some components I left out like the M1DBH because I know I need them.  If there are any suggestions regarding power and component mounting, any feedback is welcome.
I thank you for your time and can't wait to get started!
1. Honeywell is a good choice.  Nothing wrong with the GE/Interlogix wireless system, either.
2. None of the Elk keypads include a speaker for voice announcements.  The KP2s make it easy to add a speaker behind the keypad.
4. The M1XOVR has 8 voltage outputs and 8 relay outputs.  The voltage outputs can handle things like lighting up a LED, or activating a small relay (like an ELK 912 or 924).  You'd want to use the relay outputs to control anything that uses a different power supply or presents a heavier load.   The M1RB can be used with the M1 or with the M1XOVR to convert the voltage outputs to relay outputs.   If you want 8 zones of irrigation and 8 zones of lv lighting, you'll want a M1XOVR and a M1RB.
5. You'll probably want an M1XEP no matter what for doing M1 configuration.  There are dual mode communicators that connect to the phone line outputs of the M1 and simulate a phone line connection even though they really use the internet or cellular communications to contact the central station.
6. I don't know of a kit that includes a KPB.  The M1GSYS4 includes the green back-lit KP.
7. If your current draw is over 1.0A, you'll need some kind of aux power supply.  Elk makes several, such as the P412 or  P212S.  You'll need to order a separate TRG1640 to power it.   Another solution is an Altronix AL400ULX series power supply.   These get wired directly to 120VAC and don't need a transformer.
8. The Elk 14" can will fit up to two 9Ah batteries (eg PS-1290).   You can wire a pair of batteries in parallel for more run time.   As you go above 9Ah, you need to consider the length, width and height of the battery.  A single 12200 (20Ah) battery will fit, but it's a pretty large beast (7.13" w x 6.57" h x 3.0" d).   How long a given size battery will last depends on your power load.  You can always put batteries in a separate enclosure, like an Altronix BC600.
Thank you RAL for the response. 
In regards to #7, I was at 1.6amps without a cellular backup and after looking at that, I would likely use the uplink 4500ez with a M1XSP.  Would the Altronix AL400ULX provide enough power along with some head room? Should I consider an AL600ULX? Is it even possible to power an Uplink via the ELK?  This should be the final piece of my puzzle! Until I start installing anyway!
The Altronix AL400 is a 4 Amp power supply, which should give you plenty of room for growth.  The Uplink requires 500 mA when transmitting, so that would still leave you with room for growth in the future.
I wouldn't try and power the Uplink directly from the M1 unless you have very little else being powered by the M1.
One of the tricky parts of dividing up the power load between the M1 and an aux supply is trying to balance out the loads so that the M1 battery will run out before the aux supply battery.  You need to consider maximum current draw so that you don't overload either supply when everything requires power at once.  But many things, such as the 4500EZ, motion detectors and smoke detectors draw very little power most the time, and that lower current draw will affect how long the batteries last.