Speeding charge on the A9 - some questions

[jukeboxs]

I have received a "requirement to identify the driver" notice from Police Scotland, in compliance with the terms of Section 172 of the Road Traffic Act 1998.

Looking for the forum's guidance please (as I've never been charged for speeding before, and the rules seem to have changed in recent years - now much more expensive!).

Details:

• Offence: doing 56 mph in a 40 mph zone, supposedly on a section of roadworks on the A9 (standard limit 60 mph)
• I think this was an average speed camera (as offence location states: "A9 SB Bankfoot 500m north of Bankfoot north junction to 430m south of B867 junction"
• Leased car (BMW 520d) - notice received 1st December, dated 28 Nov, with offence dated 4th Nov (22:41)
• No points on license currently
• I don't have a dash cam (sadly)
• I was returning from a 7-hour round trip from Glasgow to Elgin, and don't remember the circumstances at the time (e.g. visibility of the speeding signs, whether there were roadworks on this section of the A9, etc.).
• I don't normally drive at excessive speeds (e.g. I do 65mph normally on the motorway - party for fuel economy). If the facts behind this fine are correct, it would have been because I didn't notice / see the 40mph signs, and thought it was a 60mph zone.

From my own reading:

• 56mph in a 40 zone only just takes me into Band B (i.e. more expensive than Band A)
• Speeding penalty for Band B 75-125% of weekly income with 4-6 points on license
• The notice should arrive within 14 days, however there is flexibility around this for hire cars (I assume also for lease cars)

My questions please:

1. Is there any scope to challenging the notice on the grounds that it arrived after 27 days, well after the 14 day window? [E.g. should I ask Alphabet when they received notification from Police Scotland as the registered keeper?]
2. The fact I've been apparently clocked at 56 mph seems quite suspicious to me, given this takes me only just into the Band B bracket. How could this be challenged?
3. I assume it's worth asking for photographic evidence of the offence details? This may be provided as standard when they eventually issue the fine / proceedings.
4. How do they derive Weekly Income (for setting the fine), and indeed the points to allocate?
5. The maximum implied fine for Band B is 125% of weekly income (this could be over £1-1.5k), which seems excessive. As such, is it more common for accused speeders to seek legal advice to challenge these? I might do that (e.g. Which Legal or Just Answer Law).

I thought I might take a drive up to look at the current signs at that section of the A9, although as a month has passed this may be a waste of time (anything could have changed since then).

I realise speeding should incur a fine, I am more concerned that the 40 mph signage was inadequate, and the 56 mph statistic seems quite a coincidence.

Any advice you can give (from knowledge or own past experience) would be greatly appreciated.

Thanks in advance.