-Is it possible to create more than just wooden and bone bolts at a crafter's workshop?
-Can ammo be made of practicle any metal or material for that matter?
Even without smelter mods, you can order bolts of any [AMMO] metal at a forge. Modding [CAN_STONE] onto bolts may allow obsidian.
-How can I make it so that when wild animals spawn that they will automatically seek my inhabitants?
Well, [LARGE_PREDATOR] without [MEANDERER] should cause them to make a beeline for the nearest dwarf. With both, they'll often be diverted by meandering; the curiousbeast tokens may cause periodic de-diversion, producing an intermediate hunting pattern.
And not dissapear over time due to over hunting.
I don't think wild animals breed, they spawn - so there's a constant "birth" rate, and hunting only affects the death rate. You can adjust the "birth" rate via the [CLUSTER_NUMBER] and [POPULATION_NUMBER] tokens, though according to the wiki [LARGE_PREDATOR] will severely curtail those numbers.
-Does ranged ammo always have a chance to pierce a creature's body, and thus always hit a major organ causing death no matter how light the wound is?
Since all ammo deals PIERCE damage, yes, but it's totally moddable. Switch them to BLUDGEON to work fine on undead but take a lot of shooting to wear down a megabeast, to GORE for lots of pain and bleeding without organ crits, to SLASH for limb-sever crits instead of organ crits, etc. BURN and HEAT may be dangerous, COLD would be funny.
-Is it possible to have clothing to be made only of one material?
Sort of… some can be modded out. Removing the [ARMOR] token from metals will prevent their use as armor. This does get rid of all the good armor, though(it seems all nonmetals have the same low [BLOCK_PERC]).
More dangerously, pig tails and rope reeds can make thread because they have the [THREAD] token, cave spiders of all sizes make silk webs because they have the [WEBBER] token, and shells come from creatures with the [HASSHELL] token. Leather and bones are the other way around, adding the [NOSKIN] token makes a creature produce no leather, and similarly for [NOBONES] and bones. Wood can be eliminated by moving matgloss_wood.txt to another dir entirely. However, these eliminate the
materials - you'll have to do something for woodless beds, and I think strange moods will still look for plant cloth/silk/shell/leather/bones, and if you cut clothes down to cave spider silk you won't be able to make quivers, you'll have to import them from goblins or the like. (Which can be fun, but can also be "fun".)