I feel like I've started a long journey...

Roonie, You are overproofing you sourdough sponge. Sourdough fermentation is less forgiving than commercial yeast fermentation. It is time contingent, temperature  contingent, and feeding cycle contingent. Take care of your statret as you would a baby, and this baby will grow stout healthy, and you'll have good sourdough bread.

that your starter - at the ripe old age of 7 or 8 days, is still more of a culture.

I have recently been told by a couple of well qualified artisan bakers that the culture will bubble and may even rise a bit, but one should wait a few weeks until it is a properly mature starter.

Fits with what I experienced many long years ago when my starter was young.

Hope this helps.

So, I've done the sponge overnight.  I used 2 cups starter, 1 cup water, 1 cup white unbleached flour.  That doesn't seem right straight away.  It was a little frothy and bubbly in the morning,,,, spongey. : )

Lets look at that mixture.  When feeding a starter it is a good idea to feed at least the same weight or more of flour than that of the starter.  Same principle with the sponge but using cups is volume, one cup of flour is not equal in weight to one cup of water, it is less.  So with this feeding as the yeasts increase, the food is decreasing.  not good. 

I suggest this...  first we return to a small managable amount, then feed.   Feed this 1:2:2 every 12 hours for a two days and record the improvements.   With the next 12 hour feeding reduce the starter to 20g and feed 40g water and enough flour to make a thick paste, like toothpaste, this is roughly 100% hydration.  Check it with a scales.  This will be done for the next few weeks, twice a day, morning and night.  The discards can be thrown into a container and used to flavor recipes or it can be composted or diluted and washed down the pipes. 

As the weeks go by, you will find that you can reduce your starter further if you want to 10g you may find a ratio that fits your kitchen temp and flour best.  Starter to water to flour   (S:W:F)   as 1:2:2  1:3:3  or 1:5:5  When you want to bake with it 100% is easy to calculate.  

Example:  Say you are feeding (1:2:2)  20g (2 tsp starter) with 40g water and 40g flour (total of 100g) and want to bake a recipe calling for 150g of 100% starter.  Save twice as much starter when discarding to feed 40g starter with 80g water and 80g flour to stand overnight.  Take out 20g to feed and set aside.  The rest you can use in your recipe, a little is left over to pitch or add to the discard pile or spread thin to dry as a back up starter.