Lots of feedback, that's great!
Regarding shotguns, I have started making the "XAE_Alloy_Weapons" mod, which has the alloy shotgun inside. I think it will become a new tier of weaponry before lasers/gauss.
The elerium explosive mod I had been working on will become elerium ammo, with elerium incendiary damage for pistol/rifle and elerium explosives for the cannons/rocket launcher. The projects will be batches so that you can produce more than one clip per elerium unit for pistols and rifles (since otherwise it would be useless), but fewer shots than regular ammo (and much fewer than alloy ammo) per clips.
Gauss weapons will also get an endgame elerium incendiary ammo wrapped up in the same expansion mod. Gauss becomes useless otherwise compared to lasers. In my current playthrough, I used (DE) Gauss extensively, especially for snipers, along with the (Elerium) lasers, until I ditched Gauss entirely because of the crappy damage type. It won't be a boost in damage compared to DE ammo (might be a nerf?), but the change to incendiary should be worth it.
About the changes:
1) I thought about letting the basic tank hulls be purchasable built already, then decided against it. I thought it was redundant since you can buy the parts. But I could easily change it. But I really don't get the space issue. A workshop provides 50 spaces. In the early game, how many engineers do you have? And assembling/dismantling a tank is a really fast project, so even if some engineers are taking a break, it's not for long. I don't think I will change that.
2) One of the first goal of the mod was to add a sniper rifle
(along with the shotgun) I have tried to make the TU cost enough (and the accuracy gain small enough) that a sniper rifle is a tool for marksmen only, for those shot that you really need to land. It should not be a good tool for rookies. If you think rookies are best given sniper rifles, let me know why and I will try to fix that. I give mine pistols or shotguns.
Also, the mod is intended to be used with the Alien Armoury Expanded, which adds a plasma sniper rifle (and shotgun). To me, that makes it necessary to have sniper rifles of other kinds too, otherwise it creates a contradiction.
Of course, if you're not using the AAE, that's different. Then you should probably just not use the "XCom Armoury Expanded" module either (since why have shotguns and equivalents for everything but plasma?). You can still use every other modules (Crafts + all the XAE Expansions) any ways. Version 1.02 will add a "requirement" for shotgun and sniper rifle equivalents so that they don't show up if you don't have basic shotguns and sniper rifles.
For me, it's AAE+XAE, or neither. Same goes with crafts (AAE UFOs + XAE Crafts, or neither). Both mods were created under the assumption of running the alien versions. I don't want to split the XAE between shotgun and sniper rifle, since the AAE has both together. It might be a little bit wonky now, but 1.02 will support running everything/anything else without the XCom Armoury Expanded, and crafts are already "separate but integrated".
2.1) The progression you have is interesting. In general it might be true that Gauss tech is more approachable (you're still sending a chunk of stuff as fast as possible to your target, just using a different way) and could be a good "tier-2" weapon. I just don't see a proper way to make lasers wait until after Gauss. Also, as it is, the damage numbers really don't make any sense if you get DE Gauss before normal lasers. It is too early in the game for the damage type to matter..
2.2) Changing heavy plasma stats is a BIG no-no for me. You just totally nerfed the aliens doing that, for no reason whatsoever. I understand that heavy plasmas need to be nerfed for XCom, but you cannot forget the impact on aliens. They need their powerful weapon to compensate for the AI not being able to properly equip aliens or properly use its guns.
Suggestions:
1) If you have a gauss alloy tank/hovertank, why would you want a cannon one? Both deal single target AP damage and the cannon deals less. I only kept the combinations that seemed sensible to me. If you are using an expensive weapon (DE Gauss, ELaser, Plasma, Blaster), you want to put it on a resilient platform. If you use a crappy weapon, it's because you are trying to be cheap, so you don't put it on a hovertank. Also, the manufacturing list with hulls, hull repairs, assembly and dismantling is already quite long. So that's why it's not in the main mod. I will add a "tank expansion" mod to do it for those who would like it though.
2) I am not a big fan of XCom cyberdiscs and sectopods for the reason that I think the aliens keep some of their cool stuff. XCom are a bunch of early 2000s humans, stealing everything the aliens do within a year, even if you have 1000 scientists working on it, makes no sense. Fancy stuff like mini-flying saucers without turrets and big walkers is too much for me. Maybe XComFan419 can take a subset of his Tank, Drones and Sectopod mod that only has the Cyberdiscs and Sectopods (and maybe drones) that is compatible with the XAE.
3) As XComFan419 said, it is impossible to have HWP (or crafts, for that matter) that pick from different ammos, unfortunately. I will eventually release 2 weapons HWPs though. However, don't expect every weapon combination to be available. It will mostly be: Smoke Launcher + weapon and Direct fire (Cannon/Laser/ELaser/Gauss/DE Gauss/Plasma) with Blast damage (Rocket/Blaster). Stuff like a Gauss/Laser tank is not really adding enough to justify the effort and extra list entries.
I hope this all makes sense. Thanks for all the feedback/interest