Visitng Zugspitze

The top of the Zugspitze is almost 3000m (9700 ft). The mountains at that elevation, even in good weather, can be chilly any time. I would at least bring a light jacket, but I can't see you needing arctic winter gear.

Hello Anushka, we were there a week or so ago, on a beautiful day, with hardly any wind. we had to catch the cog train from eibsee as the cable car was being maintained. inside the train was not cold, nor in the buildings at the top and the summit building.
most people had only a light weatherproof jacket and perhaps a light jumper underneath. while you can walk out on to the snow, you don't have to see the views.
it was about 10 deg C . as with all mountains the only way to know about the weather is to check the overall prediction and the on site action cam etc. the weather at 3000m can be totally different from lower in the towns.
if its foggy and accessing the cost and the time it takes , then its probably not worth going. you really need to have a few days available and go on the best day available, weather wise.

1) No advantage at all to purchasing in advanced.

2) Completely unpredictable this far in advanced. You can't even rule out a fresh dusting of snow, although this will fall as rain at lower elevations.

I've skied on the summit level pistes during a snowstorm and you can barely see 10 meters ahead of you. I would think that if it's foggy, it might not be worth your time.

3) A light jacket and perhaps a sweater should be fine. Unless you plan to spend several hours up there (and not go inside if it starts to rain or snow), you won't need anything else.

However... if you're dead set on making this ascent, don't try to plan the exact day without the benefit of a short term weather forecast. If possible, build a little bit of flexibility in your schedule, and take the first opportunity that the weather provides. July is usually a pretty good month for the mountains, but there's no guarantees that any individual day will offer decent conditions.

Thank you all! You've been most helpful - we'll be staying only one day in the area. Will keep our fingers crossed to have good weather but if not, whatever will be, will be! Won't plan/buy tickets in advance etc. Thanks again