Nice Hedge Sparrow! I think you're right - you'll need to try it out and see what maximum ISO you find acceptable.

As little as possible. Apart from any specialised lenses if, for example, I went shooting birds at Martin Mere, then the basic kit for an exploratory photo walk is:

K20D
16-45mm
55-300mm
40mm
Another lens - could be 12-24mm, 100mm Macro, 80-320mm or something I'm testing.

The best pictures are to be found in the most awkward spots (generally) so the lighter I travel the better I like it.

I wouldn't waste time on a mirror lens from any of the independents, but I would be tempted to try the Pentax 250-600mm Reflex Zoom. "eBay Fodder" would be the fate of any mirror lenses that found their way to me!

The shift lens needs to be used with a full frame camera, so film only for the Pentax range. Its primary use is in architectural photography. If you don't want it, why not offer it for sale here? There may be someone who does want it and could use it.

Some Ricoh lenses have an extra pin on their mount that can cause them to jam on Pentax cameras. They are best avoided, not being exceptional lenses anyway.

A SMC Pentax-M 50mm f2 should be cheap enough and a much better bet.

I presume it's a mirror lens? If so, they can be quite difficult to focus. I did have a Tamron 500mm but I was never very happy using it.

Photos in the gallery will only go full size if they exceed I think 1000 pixels, so I would check your sizing.

1000 pixels on the shortest side at 72ppi should do it.

Not very sharp, especially on the eye, so maybe some camera shake there? Good colour though and certainly 650mm pulls in the subject very effectively.

Apart from the speed, as you are advertising wedding and corporate services I wonder whether you should be showing images from these areas of activity rather than a statue in a garden/park.

One way to find out if it hits the spot would be to run a poll asking whrther or not the video would entice people to contact you or not. After all, this is its only function.

"Third party" doesn't mean other marques, it's a bit misleading because you are offering an image taken with a Minolta 500mm lens. You can't use a Minolta 500mm lens on a Pentax camera in the normal course of events.

It might be better to talk of "Independent" lens manufacturers, which would mean Tamron, Sigma, Tokina and all the other long lost names that do or did make lenses for pentax as well as all the other marques of the day. This would even include some marques such as Zeiss, who do make Pentax K fit lenses.

I've had a look at the image link and it's nice and big in the frame, although I can see why you like colour saturation. It comes over to me as a bit over saturated but I have no means of judging what the original bird looked like. Unfortunately it doesn't tell Pentax Users much about lens choice as the images being compared are so unlike each other and the Minolta lens couldn't be used anyway.

In Photoshop Hue/Saturation. Click Colourise and adjust the sliders to suit. My personal choice is a hue value of around 25, but it depends on what sort of sepia tone you like.