Because I'm not both perhaps?

I see your adding the rear flange distance now (Your original definition only mentioned the length of the lens) Mine is ~95mm with both caps on.

I guess the 500mm Newtonian telescope I have is actually only telephoto if used with an eyepiece (and the camera of course) - it must be about 1m long

[pedant mode off]

Time for bed.

So my 100mm macro stops being a telephoto if I focus close-up?
The F 100-300 is only a telephoto when zoom ed to beyond 170mm, whilst several of my 50mm lenses are telephotos at least when focused on infinity...
I think you'll find it's one of those words here the definition has changed. In a similar way that many companies sell 'macro' zooms that can't even get near to 1/2 life size on the recording medium - true macro should be 1:1 or closer.
At least with the changed definition of telephoto it improves the usefulness of the term!

One quick check you can do to investigate IR sensitivity of a camera is photographing a TV remote (being used)
If the camera is sensitve you see a bright spot where the remote is sending it's signal.
I checked my K100d with this before splashing out £10 for a R72 clone.

Definitely to the right of center, so it's looking into the frame.
Great set anyway!

There are 'auto bellows' but I'm not sure if there are any with the electrical contacts. (My Panagor set being a cheap example)
Auto in this case being that they pass through the aperture control levers of the M & K series lenses.

With the extension tubes it might be worth considering M42 & reversing adapters, to increase further the range of budget primes to select from. Even the cheapest (~£2)adapters should be OK for macro, but any lens you use will want an aperture ring.
(It is actually possible to tape/wedge the aperture lever on the back of the lens to adjust the aperture without an aperture ring but it's not worth the effort!)

If the budget is really tight the likes of the Pentax F100-300 would make a reasonable compliment to the kit lens. Mine was £70 last year.
The gap between 55 & 100 is not to large to cover with cropping the kit image, and it can give quite reasonable results.

What a great set!

I too have a collection for different roles. In the last year I've used:
A £7 budget model that's light enough, and can cope with moderate requirements (generally fine with the kit lens).
A heavy manfrotto 058, with a fluid head - which is big, easy to adjust & rock steady, sometimes used for studio work, but really for the Long lenses especially the 1000-4000mm telescope.
A Uniloc 1500 (Benbo style) - mainly for macro where it's flexibility comes into it's own.
And the super heavy weight equitorial for the astro telescope.

All of these will be used again along with my larger monopod (when I fit a suitable quick release clamp)

I also have various table top models, clamps (G & suction), walking stick/monopod (all only used for P&S cameras), a rifle stock, and somewhere a 20 year old home made bean bag! (Used with my old ME) Most of these are unlikely to be used unless I want a support for a flash gun or other lighting.

If I suddenly receive a large windfall I may decide to replace the budget model with a carbon fiber model, but only if the windfall was well over £50,000! (too many other things to spend it on...)

Forcing a given number of posts only encourages meaningless posts. Which can make the forum more awkward to use - I use the recent posts section to check on anything new since I last checked, (which is sometimes only an hour or two earlier).
I think having a requirement to be a member for several weeks before selling would be a minor benefit (similar tothe delay before sending PMs), but I can't see any reason a newbie shouldn't be able to buy (If I'm selling I don't want to exclude interested buyers!).
There have been several forums I've discovered by Googleing for things I wanted to get. It's quite likely that I've become a semi active member of at least one via this route, even though I didn't end up buying through that forum.

I have brought & sold (prompted by a wanted post) through PU in my year+ of membership, but it wasn't my reason for joining.