Sugar – How much sugar should I put with the fruit in a pie or crumble

You didn't heat it enough. "Turning light amber" means that you want caramel. What you did instead was to evaporate water from a sugar syrup, without reaching caramelization temperature. The crystals are not unusual (at some point you get a supersaturated syrup, after enough water has evaporated), but it is better if they don't happen, so don't give them occasion (use a clean pot, don't stir, etc. I suspect the oiling of the pan is meant to reduce nucleation sites).

The recipe is a bit strange anyway, using way too much water. Maybe you can try another one, if this has negative comments. The regular recipes will use some more conventional nut instead of pumpkin seeds, but this doesn't affect the physics of making the caramel. And do yourself a favor and use a candy thermometer. There are experienced cooks who can make sugar candy without one, but if you are not one of them, you'll save yourself lots of errors (and probably enough money in expensive ingredients for the thermometer to pay for itself).

Here is another recipe for brittle. While I haven't tried to make it, I strongly suspect that they know better what they are doing - not at least because they give you the exact temperatures you are aiming for. This is a site with lots of useful tips for candy making, and if you really want to try this without a thermometer, use their chart to learn about the different stages of sugar syrup and caramel.

And choose your recipes carefully. Candymaking (both sugar and chocolate) is even more exact than baking. Directions like "put back on medium for some time" are practically useless. In order to successfully cook a candy recipe, you have to know if not the exact temperature, then at least the desired sugar syrup stage. Maybe somebody who has made lots of brittles could work with a recipe like the foodnetwork one, noticing the problems on the fly and making the appropriate corrections towards the ideal brittle mass. If you don't know what the ideal brittle mass looks like before you start, it is better not to try it that way and go for an exact recipe.

It is difficult to give an authoritative answer because who knows what a "typical" pie might be like. It might be different for every person you talk to. I will therefore answer just for myself.

All of the made-from-scratch pudding pies that I have made have been very similar- a lot of sugar and fat and some starch to make the gel. Usually recipes also call for egg yolks which also help with binding but make the pudding a little more custardy instead of just a gel.

The texture should be sliceable so that the sliced edges sag but don't flow. I have had pies that have to be scooped out which, while perfectly delicious, isn't as nice a presentation. On the other side of the spectrum is what you have- rubber- which is a great presentation when cutting but not much fun to eat.

Gradually adding your corn starch slurry is always a good idea. Often the starch is mixed with the sugar to make sure it is evenly dispersed and then added to the liquid. As long as you didn't have clumps your technique here was fine.

I don't think your expectations of a banana pudding pie or your technique are wrong. What I think is slightly wrong is your expectations for this recipe. It's "wrong" to call something a "take on a southern classic" that uses soy milk and organic margarine. The milk fat and egg yolks in typical recipes do a lot to make a smooth, custardy pudding. Doing this with different fats and soy milk could be good but I would expect it to be different.

The bananas don't have to be precooked- that would be horrible, I haven't used earth balance but if it behaves like normal margarine then your crust sounds like it is pretty normal. The number of bananas also sounds reasonable. You want a good layer but not so much that the pudding can't work in to bind it together.

Reducing the amount of corn starch a little should make the filling softer and more to your liking. You could try adding a little more fat which will also soften the pie. In the end though, I wouldn't expect a typical texture of a pie that is made completely of non-typical ingredients.