I was using the whole set of your mods (even I messed up as I read later the tank mod section not no put all of them together 
, some tanks got lost during research).
Then I tweaked the DE ruleset as I thought it was giving me issues into achieving its contents (I had already all alien captures and autopsies).
I assume the issue was as you said that the research of the engineer before the alien grenade. Some thoughts about that would be to forfeit the alien grenade research. Alien engineers are quite hard to come by (they are not found easily unless you go for base assault, in which case you should have steeped deep into the gauss/laser technologies, specially for your overfed mutons XD).
I am glad you are enjoying the mod. I have to say the current version is quite outdated. I have had an update planned for a long time but I am trying to test it, which requires a fair amount of time.
If you have no other mod that change the engineer interrogations, you can capture another one and interrogate it after having researched the alien grenade. That will open up the research project.
The idea of Elerium Weaponization (and later Plasma Weapons) is that they require you to understand a basic level, then interrogate an engineer to learn more. If you don't know how to make elerium blow up (the simplest kind of energy extraction), then you're not ready to use it to power weapons, so your researchers can't ask the right questions to the engineer, nor would they understand his answers. Thus if you interrogated an engineer before researching the grenade, you did not learn all you could because it was way above your understanding at the time. You have to get another one. It's like trying to explain algebra to a kid who has not learned arithmetic.
But it is difficult to properly implement. I have a simple ruleset, now, which does not require interrogations at all (since the original did not either) and a separate ruleset, which will come with a big warning, for the unlocks. I generally have no issue with captures and the XAE provides a few more capture tools, so I am not sure I want to make things easier. By the time you need the interrogations, you should have Mag and Scout armors, and laser/gauss weapons which make sectoids and floaters rather easy (except cyberdiscs) and snakemen manageable. It is quite doable to taser aliens, although the stun rods are always a challenge!
Seems the issue also happens with plasma, as you require the engineer again after the two tech trees are completed I think (or that's what I understood from the ruleset).
Yes, plasma weapons require you to have developed more tech and interrogate another engineer. I split the game into tiers, which require an alien engineer to progress. The order is supposed to be:
0 - Use conventional weapons (+ alloy ammo)
1 - Get basic tech by yourself through scavenging scraps of alien tech
1* - Reach a point where human understanding is limiting you
1** - Get a breakthrough by interrogating an engineer
2 - Get more tech from Elerium Weaponization
2* - Get stuck again because your understanding of this new tech only goes so far
2** - Interrogate another engineer and finally makes sense of their tach
3 - Get the final tech.
It goes similarly with armors as well, where power and flying suits got nerfed and new "endgame" suits were added to compensate.
Also I have a CTD with the small launcher upon accessing the ufopaedia but I have to check it further just in case.
Are you using the Alien Armoury Expanded? Or another mod that changes the ammunitions of the small launcher? The XAE uses 4 different ammos for the small launcher (Bomb, Smoke Bomb, Stun Bomb, Elerium bomb), but if another mod changes the item definition, that can make the UFOPaedia crash.
Then, giving feedback about your mod:
I liked your approach for the tanks and the mod in general. The salvaging and tank customization is quite an interesting way of boosting the engineering department. Then the dual tech tree (laser/gauss) is quite appealing, specially with the nice versatile variants of the gauss launcher and the laser blaster. Also, the skywarden is really cool, I loved the side doors.
Glad you're enjoying the new stuff
I tried to add variety and come up with weapons that encourage different battlefield roles so that not everyone in the skyranger has the same equipment.
About the tech tree, there is still some sharp edges such as the improved medikit. Some ufo elements can be hard to come by just by the spawn rate of some higher size ufos (luke extra ufos could help with this). Also, the manufacturing list is quite huge at the end and a little bit annoying to navigate by ( I believe some other mods I tried had some kind of sorting).
The improved medikit is basically free health (since it heals more HP per fatal wound) which also means faster soldier recovery from being wounded (recovery time is a function of how wounded a soldier is at the end of the mission, I think?). Since it is a "free improvement" over vanilla, I decided to keep it difficult to obtain.
As for the manufacturing list, I am trying to use categories and group weapons together in a consistent fashion. I don't remember the state it was in 1.03 but the next version will be relatively ordered.
Lastly, there are some elements that seems to give quite small improvement (armors and crafts) that fall in the gap of "short-term useful or avoidable by waiting the long term solution". Is it viable to use the same approach as with the HWP?
-In the case of the armor it could define a "basic armor" and then some upgrades upon it (flying, atribute and so...).
-In the case of interceptor/skyranger variants, it would be nice to "pimp them" progressively from the initial model ( I understand that the game mechanics can be unfriendly to this).
It would be possible to implement some armors as "basic armors" and then add different properties to it. The problem with that is the conversion takes a project just like the creation does, and ideally you have another project to turn the upgraded one into a basic one again.. Maybe I could make it such that all corpses from one category can only be repaired to the basic armor, which would remove some of the repairing project and then you have to re-upgrade the armor (costing more materials). Overall though, that gets into the "more bothersome for the player than anything else" territory.
As you suspected, it is impossible to upgrade crafts through manufacturing. Once they become a craft (from "Skyranger" in the purchase menu to "Skyranger-2"), they are not really items any more. Just like soldiers.
Last but not least, I would like to say I appreciate your approach to the modular modding. Your code is very welcoming and easy to understand, which helps a lot in learning the inner outs of the ruleset system.
Cool! I'm glad you enjoy it. I am trying to make things approachable and customizable (both in choosing which mod you want to use, and modifying the mods for what you like). Have fun playing around. Hopefully I can get v1.1 out soon-ish and it will fix some of the problems. And I'm always happy to add more stuff to the XAE too!
