-Doors because you said you needed them. Also going to assume you don't need any other fun pieces like tires or transmission or cooling system or anything like that. I think there was a guy in Florida with a set of doors he was looking to offload. Probably gone but I'd look for those. Also GET NEW HINGES.
-New Puma-style exmoor seats. I think all the Puma NTOs are gone so this is next best. Also get heated elements in them. Seats has been one of the best upgrades I've done and heated seats are awesome. They are so comfortable its amazing.
-LED headlights. At night time, they've been great. I recommend Peterson 701c headlights (get them off rock auto, get discount code elsewhere on this website. After switching, my aux lights have become redundant, I don't need them but I love having extra lights on my car. They are literally better than a 20" double stack LED light bar on back roads.
-Consideration: Block heater. If its truly cold where you are, this will be a significant help with cold starting.
-Allisport VGT turbo and intercooler. Big time TDI upgrade.
-Since you'll already have the car at the paint booth, get the interior and floor coated with Al's Heat and Noise Reducer (its like lizard skin, but not stupidly priced). Just do the whole interior from the dash to the back. Pull up carpet and do that. This will help with noise and insulation. Definitely have it sprayed in, I roll/brushed the front seat area in mine and FML that sucked.
-Rear Tire carrier. Takes weight off the rear door. Very nice. Once again I'm sure this is available here in the US, but couldn't find it off hand.
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-(Personal Preference) Front recovery point. I think every vehicle should have a front recovery point and its weird that Defenders and series trucks really don't have recovery points standard. So something like this would be cheap and easy for you to install in your driveway with a helper. I'm sure there is a US distributor for these, I just can't find them. But this little guy seems to be quick and effective.
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You are in NJ? I would say Red Door Rovers over in PA. I've visited his shop, he seems super legit.
Somehow this will probably be over $10k but pick and choose what works for you. Anyway, I envy you have a budget like that to spend. Should make that truck a ton better.