Hi Hanekem. You are correct regarding the chemical fuel consumption in the solid fuel rockets. The game does not allow consumption of more than one type of fuel... sadly. If it did, I'd have ships consume Uranium, Oxygen, Water, Solid Fuel, Food, and a bunch of other things representing general maintenance and repairs and consumption.
I think that much detail would be a nightmare, even if possible
So the only solution is exactly as you suggest... have it approximated by increasing fuel useage of the main reactor. I've done this by having the solid fuel rockets a much higher consumption rate than they were... about eight times as much actually. Also I've doubled the energy output of reactors so that a ship isn't bogged down by having dozens of reactors to meet the output. They have the same charge capacity as well as the same fuel-to-charge rate, so the end result is that they burn fuel much faster as well as the thrusters. The overall effect is that ships now use fuel much more quickly than they did in v0.1. Due to solving a higher-than-necessary fuel cell capacity, I have also nailed down an issue that was creating drastic fuel shortages in early-to-mid game when a player begins to really start pumping out ships and stations.
That is an interesting change. I think refuel needs to be something periodic, otherwise the resupply ship is completely useless (actually I've never used it in vanilla)
The concrete bunkering I tried exactly as you said and it still kept favouring the concrete bunkering. In the end I did a hybrid option, where the armour was put in preference to the other armour in tech level, however I replaced it with a new type of armour called Plate Steel armour... it is basically just solid steel. Basic. Simple. Expensive as hell if you want to produce a lot of ships and stations clad in it. It is easily and quickly replaced by the update of Heavy Alloy armour, and then gets into the previous version of Layered Mass armour which starts to diversify the resource requirement and begins to produce some really efficient armour results.
It doesn't do quite what I was trying to achieve by introducing Concrete Bunkering (ie: use concrete resource instead of steel resource, and free steel demand up for other applications instead) but it will do. A player will find that their steel demand quickly sky-rockets unless they research a replacement for Plate Steel armour early in the game.
I'm fairly happy with this end result, and it is included in the v0.2 update which is being released now.
So, given that there is only one armor at the time in the base game, odds are the AI isn't prepared to choose armor by any other factor than its Armor Factor.
So, by that assumption, the AI will probably only be able to use one armor option at the time.
If you are still having issues with Steel demand, perhaps the solution could be in making the resource more abundant, both in quantity of sites and percentage.
About the aliens you wrote, they sound interesting, but I am not a fan of super bio-tech. Not because it can't be interesting or varied, but because to get high end performance you need to redefine Biological, at last as we understand it, and end up with something that looks biological, or has a biological coat, while it performs like non organic materials (Had enough to be compared to metallic alloys, or generate enough electricity to compete with a fission reactor, and superconductive materials to make it all possible)
Spacebugs are a trope of the SF setting, yes, but I personally prefer the bugs to be tool users, because otherwise we need to do a lot of mental gymnastics.