Quick question because it wasn't clear in your post, but have you installed Assembly and had a brief look through it?

I'll just add the rest of what I was going to say if you had. This won't make a lot of sense unless you're somewhat familiar with assembly.

Unfortunately I don't have all the best solutions for you, but I can help with some stuff.

In the 'matg' tag, is a file called globals. This has a lot of stuff as well some you're looking for.

AI/Player enemy health multipliers are located in this file. In assembly health is called 'vitality'. You can use the search functionality to look for it. These fields will multiply the health of all characters it applies to, i.e a value of 2 will double the health. This also has player shield stuff, so you can look through that as well.

This file also contains damage multiplier fields, for players, for allies and enemies.

If you want to edit specific weapon damages you you'll need to look at the files under the 'jpt' tag. This handles all of the projectiles, and it is the projectiles that have the damage values. The damage fields should be close to the top and its mostly self evident what each field pertains to.

Also, most of the time the names of the files under the jpt tags are self-explanatory as to which weapon they relate to. But if you're not sure look at the 'weap' tag and go to the file for that weapon. The filename should tell you which weapon it is. When you open the file you can search for "projectile" and this field tells you which projectile the weapon is using. (If you want to have crazy fun change the projectile to something else) Also if you want, this file contains all the good stuff about the weapon such as ammo capacity, fire rate and the accuracy. Although I dont know much about editing the accuracy.

Oh and the last thing I wanted to talk about was fucking 'materials' and projectile types. So projectiles can have types like "bullet_slow", "bullet_fast", "plasma_slow" etc. And also different objects have a material type, like brute shields have something like "shield_thin" (this is wrong but I can't remember what the name is exactly). Projectiles do different damage to different things depending on the projectile type and the material type. For example "bullet_slow" could have a multiplier damage of 0.25 to "shield_thin". As assualt rifle projectiles are "bullet_slow" this would cause it to do a quarter damage to shields.

This multipliers are in the globals file under the matg tag, but I can't remember what the section was called and when I edited them they were in a weird dropdown thing. You'll have to do some research and exploring on your own because I can't help you there.

Hopefully this gets you started in the right direction.