I'd opt for choice d) but I wouldn't bother installing to 270mm thick anywhere. See this thread...
https://www.diynot.com/diy/threads/free-loft-insulation-questions.493394/#post-4041723
Mine is an ethernet module add-on which costs about £50, is hard wired into the alarm panel, and is connected to my internet router by an ethernet cable. I have full control of my alarm panel via phone app or any internet - as if I were standing at my keypad in the hallway.
The Selfmon service...
Here's a link to the installation manual...
https://static.premiersite.co.uk/24498/docs/1758647_2.pdf
If all else fails you can buy new G2-12 panels on ebay cheap.
BTW there's a service where you can monitor the G2 alarm for £1/month, so you can control the alarm from a phone app, and you get...
I'm not an alarm expert but I have a G2-12 which I self-installed with some help from this forum. I'm pretty sure you need to buy an additional bit of kit to expand the G2-12 to be 20 zone - would this explain the extra £50? I don't know about the MK8 keypad but be aware the MK7 comes in two...
Sorry for late reply. I cant help with your specific question but my panel is version 1.52 if it's any help. I'm sure SM Alarms will be able to help :)
If it's any help I've had the LCE module on my G2-12 for a few years now, and it works perfectly.
There is an iphone/ipad app, which I use.
Google Selfmon, which should take you to SM Alarms.
Beware some consumer units are "split load", ie there are two sides/halves to it. It's quite common for one side/half to be RCD protected but not the other side. Check whether yours is all RCD protected or not.
The ones I've used look like this...
https://www.ebay.co.uk/itm/Adjustable-LPG-Propane-Gas-Regulator-Calor-1476P-Max-Inlet-20bar-Out-0-3-0-7-bar/303093052456?hash=item4691c0f428:g:ZlAAAOSwaeVcW1ke
And screwing the thumbwheel up or down affects the amount of flame.
Iron straight onto the existing edge. Use a cloth between the iron and the new tape. I found the best finish was to deliberately leave it with an overhang on both edges and cut the excess off with a stanley knife.