Stuff inside the engine cases I always use loctite. Last thing you want is a screw coming loose and rattling around your clutch or something.

External stuff I don't bother so much, as that's easy to enough to spot and rectify.

My DT sounds really loud to me riding it, but like @Calum says, it doesn't carry. I've seen videos of me riding past someone and you can barely hear the bike lol

I know the DTX springs are progressive, so if you found a set of them they ought to fit

Some heavier oil will help, but a fork conversion is probably the way to go

I've got some eBay specials on mine, they were listed for the DT230 but fit ok.
Might fit the DTR as well?

Yeah definitely should be a plug in there. 1 or 2 cables for the starter solenoid (to spin the starter) and then 1 or 2 for power to the rest of the bike

Haha great idea

That's looking sweet!

What crash bungs are they?