1) It would be beneficial to leave as there is no way of determining whether this is 50mph or NSL due to lack of signage at either end. Likely NSL, but needs confirmation from the council.
2) This is more likely a missing case of NSL repeaters, as I remember there being no speed limit signs around the roundabout on the A24. Again, this likely needs contact to the council about missing signs rather than assuming it is 30mph.
3) This is incorrect. The A24 is a dual carriageway throughout, despite the large gap between the carriageways. The 60mph signs (not NSL) southbound confirm this, as do multiple blue circular arrow signs with a plate reading "Dual carriageway"