More food for thought:

I considered the Perry Vale car park for the preferred Leisure centre site, and it is a very tight fit (pools end to end maybe?), remembering we need to keep a road through to the industrial estate. But there would be very little parking area left.

I do not think you can get away with providing just the few spaces in front of the station for parking.
If you could get away with it, Lewisham would have sold the PV car park off years ago for development.
In any case one objection to the council's proposals was the lack of a parking area. Sorry - this is not my preferred option.

The Centre should to be located on the East side of the tracks, as land prices are cheaper. Sited next to something unpleasant will reduce the site price even more and there will be less restrictions on design.

The portacabin site is next to the South Circ, the railway, and a grimy underpass. And it is close-ish to the station/centre. It is near perfect although slightly small. On livesearch, link there seems to be a garage and some general garden area immediately behind, that might also be need to be bought.

I think this proposal would be more in line with the UDP, which wants to make more of the centre of FH. The Council's report on their proposal had very contrived links to the UDP - the truth is that it does not tie in very well at all.

Size for size, the current pools site and the extended portacabin site are equivalent, so morally we are not eating into the glebe land we have inherited.

Of course Louise Hse needs to remain as a community area - Lewisham is desperately short of study/computer areas, the few provided often over flowing (youths even daring to sneak into the local history room in Lewisham library).
The computer facilities in FH library are always full, so there is a local demand.

This would be appropriate use of the building.