It is a lot more than hundreds. Let's say you want to make one new rifle type. Those frames need to be in every character animation that can use the rifle. Looking at my spreadsheet of animations, there are 27 characters that can use rifles.
Now looking at one set of rifle animations, there are 9 sets of required animations: stand, walk, take out, put away, parry, point, unpoint, fire single, and fire burst. And each of those is multiple frames in sequence, and also 6 directions. If I deconstruct just one of those character's rifle animations I have 68 files.
So, in order to add just ONE new rifle type, you have 27x68 = 1836 frames to make. And you wanted to do what 10 rifles? 18,000 frames? Manually?
There is another problem, the engine has a fixed number of animation codes. J suffix is rifle. They are file name suffixes D (knife) through M (rocket). I have tried adding new codes past M and they did not work.
Corpse had a brilliant idea for adding new codes though, you basically clone the character into another name, and a script can then do the art_change_fid_num to switch to a new set when wielding certain weapons. This is all untested and conceptual though, and it would require a lot of new scripting.
So overall I think its pretty unrealistic to do what you're suggesting, and not much bang for your effort. I suggest that there are many other things that can be "fixed" that would be much less effort for more overall impact on the game.