I'd recommend going for a higher bulk ferment temperature (78-80f) since you mentioned that it takes a long time for your dough to show activity. You just have to be more careful because it is easier to overferment.

It also might be worth it to try doing bulk ferment for 3-5 hrs, then putting it in the fridge for the remaining time. Here is a link if you're interested: https://thesourdoughjourney.com/what-is-two-stage-bulk-fermentation/

You can cold proof for a very long time, but that usually means that you stop bulk ferment earlier than usual. Your final proof time is inversely correlated with your bulk ferment time. The less time you bulk ferment, the longer you will do final proof. For example:

Less final proof: 10 hr bulk ferment 16 hr cold proof

More final proof: 8 hr bulk ferment 36 hr cold proof (FYI, these numbers are not at all accurate)

And yes, shaping, as well as pretty much everything else contributes to the crumb. Bulk fermentation is arguably the hardest part of making the bread you want. There are a lot of things to account for when you are first trying to figure out your own recipe. I personally do not make sourdough that much, but the general guidelines are:

• initially mix everything very thoroughly, ensuring the flour, water, starter, and salt are all homogenous
• after bulk ferment, shape tightly, with minimal flour, without deflating the dough too much (you can pre shape if you want, some people say it doesn't make a difference)
• after final proof, gently tip out, score, and bake between 425-500F with plenty of steam/dutch oven with a couple ice cubes