If the extension tubes support the electrical connections lighting can be done easily & reasonably well with TTL flash. Either off camera (arms reach away typically) or bounced via a suitable placed white A4 card.
With the option to check trial shots, working out manual settings shouldn't be too arduous for simpler tubes or bellows.

Note most bellows loose the aperture control linkage that closes down the aperture as you take the shot. This makes the use of a tripod pretty much compulsory, as there isn't enough light with the aperture closed to frame/focus.

K5 & possibly more - 30mm f1.4 appeals most.
I'm not too concerned about the lenses though.

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I've switched from a neck strap to a hand strap (video camera style) which I find a great improvement. Now my camera only swing around when my hand does...

I use two general photography forums. These are the grandly named 'World Photography Forum' and 'PictureSocial'.

I also occasionally use some specialist forums:
MFlenses (Manual focus) - which I find good for infra red & UV photography
photomacrography (microscope & macro photography)
along with the specialist groups in Flickr (DIY, infra red, astrophotography, pin hole...)

I find all of them rather slower moving than PU when it comes to discussions.

What if the visualisation requires a different aspect ratio, or moves too fast to frame properly, or a slightly longer lens...?

(Relocating does not always replace using the right focal length, it changes the relative proportions of near & far objects)

I prefer not to crop, my K100d only has 6MP so I've not got much spare resolution. But sometimes to get the shot I'm after there is no choice.

Sometimes I see something new when the image is on the screen, & wish I could crop to a reasonable resolution of that portion.

I beleive the hot mirror on the K200d is significantly stronger than the K100d. But it should still be capable of giving you a chance to play with IR. You'll find it requires longer exposures, but you often want to use a tripod even with the K100d.

Filters can be had for under £10 if you're willing to wait for the variable international post, so it's not an expensive mistake if it's not practical.

Several of your older lens will probably have an IR focusing mark as well, which should simplify things.

The basic filter will work fine with the *istDS. I use several cheap chinese ones (different sizes & wavelegths) with my K100d. A little variation in your normal framing technique may also be required as you don't see anything through the viewfinder. (Tripod - frame shot - filter - shoot or aim without the viewfinder either way cover the viewfinder to reduce stray light)

I find focus & exposure can need a bit of trial & error, & it can be difficult to judge what scenes will work well in IR (I was lucky with most of the more open shots in London last month). But it's fun to play with & gives a different view on the world around you!

At higher ISO or with fast lenses handheld shots are relativly practical, this 3 shot pano was handheld:

Perhaps they should change the mount code from P/Q to PDQ!

Unlike extension tubes, with close up diopters are only any use if they are good quality ones. My old BOOTS one introduces all sorts of aberrations.