I was briefly a Geology Major long ago so some info may not be up to date.

1a. A quick look at that last glacial maximum shows time frames on 10’s of thousands of years. So the ice would be accumulating for around ~10-15 thousand years then declining to where we see it today possibly.

1b. Sounds about right. The “warm season” is not sufficient to erase the previous winters snow fall. A lot of these cycles seem to work on positive feedback loops. More ice > more light reflected back to space > colder weather > more ice etc. the condition will accelerate its effects until another factor steps in like natural variation in the earths tilt and orbit, or volcanic activity etc. which may cause a warming cycle to begin causing the ice age to diminish. Technically I believe we are still in an Ice Age as we have ice caps where as in the distant past earth did not have such caps year round possibly.

1c. Less significant variations than you may see today across the globe seems to most plausible.

2. Weirdly most glaciation happens on land and land is mostly in the Northern Hemispheres. The glaciation would of had effects globally. Lowered sea levels had caused England to have more landmass and possibly even connected Australia to New Zealand by a land bridge now submerged. They would of had a wildly different ecosystem than they have now would be my guess. But they may be the reason they have such unique animals today.

All very cool questions. Keep on digging.

Piggybacking on that I seem to recall that charcoal remains of fires can be useful. We figure the tree that was used might be in an average age range for that tree narrows the window down considerably. Often times these sites were used for gatherings or ceremonies so they would use fire to cook and for warmth etc.