Kneading causing gluten

To be precise, the lollies are not melting. They are absorbing water from the air.

If you're really just crushing the lollies (not melting them and re-casting them into sheets of "glass") then you're accelerating the absorption process by increasing the surface area.

Does it need to be out in the open for five days? I'm surprised the gingerbread hasn't gone soggy (actually, I'm surprised it's not been eaten). I would consider putting it in an airtight box until it's ready to serve.

Otherwise, you might be able to make the windows last longer by reducing their water content. Put the crushed lollies in a pan, bring them to the boil and let them simmer to lose more water. Use a sugar thermometer to find the necessary stopping point. Be careful not to burn the sugar. Then pour onto a flat greased surface, to solidify into "glass".

Some answers to your questions, based on my experience with wild sourdough starter in San Francisco:

• 70-80F is the ideal temperature range. Below that the yeast incubates very slowly; above it, the starter will tend to ferment alcoholically.
• Do not leave the starter in direct sun. UV light is a powerful sterilizing agent.
• An organic, cold-processed (i.e. stone milled) flour works best, because it will retain the maximum amount of its own wild yeast on it. Cheeseboard: Collective Works likes to start with rye flour and gradually add bread flour, but they don't give a tested reason for this.
• I have never heard of using fruit juice in a sourdough starter. I would be dubious about it; you'd be likely to end up with vinegar.
• Sugar is unnecessary for sourdough starters.
• Use purified water; chlorine/chloramine/ozone in tap water can kill your starter.

Finally, starters incorporating milk are fridge-only starters (as opposed to flour-and-water starters, which can be kept at room temperature if split frequently) which depend on the bacteria and lactic acid from the fermenting milk for part of their sourness. They can be effective, and actually a good choice if you live somewhere with weak/poor wild yeast. Note that you cannot transform a milk sourdough into a water sourdough, and using up 2 cups of milk every 2 weeks is more expensive than 2 cups of filtered water.