Hi there Harty.
Saw the ad for the WR-R on the HUBB, then quickly went away again because it looked far too nice
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I did my screen myself with sticky vinyl/Fablon.
Speedblocks were done by my wife with a desktop cutter/plotter, the rest is just hand cut. Took a while and there's a few imperfections when you get up close, but still a lot easier than getting paint to stick to the plastic, and it only cost a few quid and a few hours to do.
My bashplate is the Yamaha option one - was on the bike when I bought it second hand, but I don't think they are that expensive. Has taken everything I've thrown at it, including grounding on rock steps on Stanage Causeway. The engine bars are Yamaha as well, but I don't think you can get them any more.
Virtually any high mudguard can be made to fit using the bolts for the towing eye. Mine's an RMZ450 one. They'll generally need either trimming a bit or some spacers under the rear mounts to make it clear the radiator.
Here's mine as it stands today, with an MTC single exhaust, and home-fabricated undertray and tail-tidy (and, ahem, a few other subtle non-standard bits).
The only things on your list I haven't done yet are the 18" rear and the seat - although I'll be going the other way with the seat, adding height to allow me to get further forward for rallying.
Talon have a spec for an 18" wheel setup, having made one for Jenny Morgan's bike when she did the Heroes-Legend. I haven't dared phone them up and ask how much it would cost for one though
. TBH it's not that bad with the 17", and there's enough decent tyres (Mitas C-02, Army Special, etc) available to fit that will handle everything I've done with it.
Hope you enjoy the bike!