$3000 is probably a bit much for an R model but like you say its you dream bike so it doesnt really matter.
I have had no problem at all getting any parts for either of my NSRs and as you probably know Charles one of the moderators of the site and his girlfriend both race NSRs, and there are plenty of American owners on the forum, so getting parts isnt an issue as i beleive most of the parts for the 21/28 are still made.
The bikes themselves are razor sharp and will out corner just about anything, and set up correctly you can happily seee a steady 63BHP and not compromise any reliability.
As you already own a Honda you are aware of the top build quality so you know you have no worries there.
There are sooooooo many upgrades that you can do, SP suspension, USD forks, Tyga stuff, HRC kit, it's all available so you can either leave it totally standard or...............well that depends how deep you pockets are
Welcome to the world of the NSR250 you wont regret it.
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MC21SP - Roth-tax
CBR400 - track
MC21R - sold
MC21SP - sold