My Defender is a 1996 90 CSW 300Tdi.

The driver's interior door handle has always been a bit 'flappy' and ceased being effective a few months ago. As I suspected, it's fixings are slotted and these were loose meaning that the rod that the handle operates is not 'tight' to the door catch (it has play in it). The plastic 'nutserts' (part MWC1950, I think) that hold the door handle assembly to the door seem to be stripped and therefore incapable of holding the handle mechanism tight (and effective). YRM seem to do some reasonable replacements (£2.95 + VAT for 10).
Question 1: Does anyone have any advice (other than straight replacement) for the most effective repair?

Several of the 'fir tree' door card clips are broken. These appear available on eBay (I won't use eBay for critical parts, but I'm not fussy about trim if it looks correct). However, I'm not sure how the white part (the part in the door card that the black 'fir trees' clip into) is fixed in the door card.
Question 2: Does anyone have any advice etc.?

The vapour barrier (which is really just a polythene sheet) is tatty, so I'm thinking of replacing it with some heavy duty builder's polythene with either new butyl strip or gaffer tape.
Question 3: Does anyone have any experience/advice etc?

I was planning to change the door locks and I plan to drill a hole in the steel panel that holds the window regulator ( a 'trick' from the guy from Britannia Restorations on YouTube) in order to undo the screw directly without removing the window regulator panel assembly.
Question 4: Does anyone have any words of advice, or warning?

Thanks all.