I'll answer whatever I can. I'm semi-competent at the game myself though I've yet to reach end game on any character.
1. Levelling up your skill and books are the ways you'll get 99% as far as I know. One uncommon way ia getting sd cards and using the ink tablet. They have music, photos ( morale boost ) and sometimes recipes ( mostly food ).
2. It depends. I think INT also influences it but I don't know the definite chance or if it exists. I don't think I've ever tried any recipe that was higher than 1 level than my lvl so I can't say. Just do the recipes on the same level your skill is. I think the biggest factor on skill exp gain is crafting time ( and focus obviously ).
3. I believe crafting used to raise both the main and secondary skills but that was removed. Only the main skill gives exp. No clue what you meant by the fabrication bit.
4. The only use I have for chemistry set is for making the onboard chemistry lab since it has built-in water purifier.
5. You could try to jackhammer throigh it. Be aware the roof might still collapse but it probably is safer than just smashing it. Alternatively build a wall right next to the wall you want to destroy to possibly 'strengthen' it. No clue if that will work.
6. Small animals won't give you fat ( you craft it into tallow with water ) so try a moose.
Have a fun death
7. Never had that trait so I can't help you with that.
8. If you're lazy like me every 2-4 weeks seems optimal. This way you should avoid upgrading to a build with game breaking bugs. If you want to know what was changed use this site: http://ci.narc.ro/view/Cataclysm-DDA/job/Cataclysm-Matrix/changes
Hope I helped.
EDIT: Forgot the latter part.
- Charcoal Smokers are rather easy to craft. I personally prefer food dehydrators ( they are uncommon but can be crafted with decent electronics I think ).
- Ammonia is somewhat common in houses ( thougn I didn't see much recently ) along with bleach. No clue if it can be crafted.
- Can be crafted, not sure about the exact skill lvl, jist get your cooking up.
- Another rather easy craftable. You need bleach ( or lye powder ) water and something else I can't recall of the top of my head.
- Break refrigerators for hoses.
- The only place I ever found sulphur is near lava. You will take heat damage so be careful. You'll get a chunk that can be crafted into usable sulphur.
- No clue about Niter. Are you sure you didn't misspell it?
- Get aluminium cans and sand ( bash sandbags in basements ) and you can craft Aluminium Powder.
- It's craftable. Get your cooking up and hopefully a copy of chemistry textbook.
- I think to get the scrap you need to disassemble damaged electronics.
- Bash ovens for some ( along with the ever useful heating elements which you should collect ) or loot an electronic store for literal hundreds of it.
Yes, there is a difference. Sewing Kit won't let you modify clothing ( also it stores less thread but who cares about that ). To refit clothes they have to be fully repaired. It goes like this:
Repairing > Refitting ( If needed ) > Reinforcing