@strangely, I’m not an Alarm guru, and this is really the first Alarm system I’ve ever had installed into a house I own. From a functionality standpoint, there are a few things that the “better” keypads have that I’d look for again in order get get higher WAF. So when you pick your Panel vendor, make sure you can get it with a higher-end Keypad as well.
The most basic Alarms have a numeric Keypad and no display. These typically “just beep” when they’re arming (etc). The next level up seem to have a rudimentary display for the code, sometimes Numeric and sometimes a Grid of Zone LED’s. Again, these often just beep, or display a Numeric code when they’re arming.
The one I have has a full Alpha Numeric display (see the wiki page for links to it on the Paradox site). It displays a label (Installer settable) along with the current status of each Zone in a Rotatating Fashion.
If I leave the Master Bedroom windows open, the two lines display something like:
010 Zone Open
Master Bedroom
and then toggle to:
Area 1
Not Ready
and then flip back to the first (etc). This is REALLY handy when you have a lot of zones (I have 18) as it tells you what’s open and/or failing. It also beeps (etc) but the above is much more useful.
All of the Labels are programmable by Zone (like above) and by Area (I haven’t bothered to set mine since I only have one area).
They also tend to have dedicated buttons for Arming (various Arming modes)
My Mrs loves this, esp compared to ones she’s had in other places that she’s lived.
From what I’ve seen, the higher end Keypads from co’s like GE (Concord 4) have similar features. Most of these can also get announce-modules that talk to you, take commands over a phone (etc) but I haven’t added any of these to mine.
I do know mine can support Smoke and Heat sensors (I have the latter right now), but apparently there’s some code that means these cannot replace the Wired Smoke sensors that CA requires. Something to be careful of as you setup your system.
other than a ton of unused telephone cables which I might be able to use perhaps to link the panel with the keypad perhaps?
I have 3x Keypads (front, garage and master bedroom), they’ll all wired with standard Alarm wiring (which is 4x conductor, and “thick” presumably as they’re carrying voltage and signals across long distances). Not sure if Cat3/Phone cable will cut it for this purpose, you’d have to check the load specs on the particular devices. I suppose you could bond pairs if you have Cat5 Cabling 
Anyhow most of the sensor inputs are configurable to handle different device types and, from memory, different styles (NC or NO) to trigger events.
Inputs can be setup to trigger a regular alarm, fire alarm (etc). There are also keypad buttons for user-panic as well.
Can the temp sensors also be used?
Not that I’ve seen, there are other Panels that do that type of stuff but they don’t have integrations yet.
It seems the alarm system is a good cheap way to get the same functionality that some Z wave devices offer.
Right, once you have a baseline platform that’s expandable, you can add a ton of stuff. I have 24-Zone setup (18 used) so have a bunch of room for expansion. I can add boards to get up to 48 Zones on my DGP (the higher models go up to 192 Zones) and I have a bunch of Wireless Zones (via an attached Magellan) for Remote Controls or Wireless Sensors (if I add them)
You can see the Markets they’re targetting with this thing.
I was thinking of adding a few [Wired] Motion sensors around the house to help trigger Scenes. I prefer Wired since there are no batteries to replace (HSM100’s burn batteries) but there are Wireless ones also that are very reliable.
If I went with the DSC stuff then would Javier's plugin work as well with SQ remote as Guessed's appears too?
I can’t comment on the comparison, but I believe he does the basics the same way I do, notably Alarm Zones become a Motion-Sensor variant in Vera. This is the key to getting the “dashboard” in Vera, as well as in SQRemote.
There’s a separate Luup thread where I’m trying to get Javier to standardize the interface/API for an Alarm Zone (for Arming, Disarming, yada-yada). Currently there is no standard, so if we can get this done then the Control Point folks (SQRemote, iVera and the Android options) will be able to build a UI that handles all Alarm Systems for Arming/Disarming (etc)…
In the interim, you can use Scenes to “talk” to our respective API’s (declaratively, no coding), and these Scene buttons can be exposed in most of the Control Points. The downside here is that “Disarm” would require you to store your PIN code in Vera, so I don’t do that (it can, I just don’t)
How comparable are the paradox systems in terms of price and features to the DSC stuff?
From what I’ve seen, the Paradox modules are expensive and the DSC ones are a lot cheaper. That said, the Paradox stuff is crazy-expandable. If I were going to build a small system, I’d definitely research the DSC options, but a key driver would be the Keypad UI for WAF.
If I were going to code another Alarm Plugin, I’d look at the GE models (like the Concord 4) or perhaps and Elk. But that’s not going to happen anytime soon