Is the slave push rod the original one? Wear can be an issue.

Connections in the fuse box common issue, try cleaning them up. Old glass type?

Probably cold rolled, likely the most available. Strength wise not much in it for what you need, but cold has a smoother surface finish. 3mm is what I use for chassis.

What vehicle/year?

The only thing I have done to sort a crunched wing id replace the whole thing with a better [not new] one. However recon you are on more of a restoration than fix up. It is not hard to remove spot welds, there are special drill bits to do just that and they work well. It is a case of rivet to...

MUD UK do a range of switches.

Me too, I went through 3 replacements in 3 months last year before I found one that worked and kept working. A new in the box original Waxstat made one. 👍

Note that is an odd one, if switched on should go at all times the ignition is on regardless as you know. All I can think is some one has wired it wrong at some time but just a guess.☹️

Usual and best place to connect in your landy is in the right rear under the cover there. And what ever you do do not use those devils inventions "scotch blocks" to link in.

Carry on with your old type bodge method if you must, but better modern methods are available today as noted by myself and others on this forum.

Model and year may be helpful.

Sounds like the type fitted to 1980 and on Series and 83-85 Coil spring models.

Hello Kiwiwolf, Welcome to the forum. Pretty sure you are correct on fan removal. However I swapped mines [ 1990 truck] out for electric some thirty years ago.

Early 80's models had the previous Series model lift up recess type handle's. Swapping the whole door for later "car" type handle with wind up windows may be an answer. Or is it you just want a better locking system? There are ways to fit central locking for old Defenders/ One Tens.

Given the chassis is already shortened you would likely have to fabricate brackets for both.

Heavy duty 25mm rear anti roll bars are available.

Its Brake not break [as in broken] Only the front "leading" Brake shoe has the pin that engages with the adjuster cam, it is also the place where the return spring hooks on behind the snail cam other end on the backplate. Rear brake shoe only has the lower spring that goes between both shoes...

I can understand those Insa turbos chunky's making a racket on the arms. For the sort of stuff you are doing as @300bhp/ton says spacers or offset rims would be fine. Bearing strain tends to be more of an issue when very wide wheel/tire combinations are fitted and driven hard. For every day off...

Issues with spacers are your tire can end to far out for the eyebrow to cover, a legal requirement in the UK. Greater stress on the wheel bearings, just something to be aware of and keep an eye on. Be aware it is not good to hold steering at the full lock position when you can hear the pump...

Before messing with the steering box do as @Dippypud notes above. Those steering shaft UJ's look rough and it is likely other joints in the system not good. Also check that steering rods are straight and not binding with anything. From Your pic looks like much work needed to sort this one.