Summarizing some info put together from research. Assuming your form 1 application has no mistakes, this is what will get you approved or denied:

Application must state- Tools and materials for construction will be sourced from local hardware stores and and online stores including but not limited to: (examples: A+titanium.com, 17-4solid-bar.com, Mcmaster.com, etc) but- DO NOT list any sovent trap companies or websites that sell any sort of half made parts! Listing any companies that sell anything even remotely looking like a part= ATF dont like it and will deny.
Once you have the approved form, you are free to buy whatever you need to build whatever you have been given permission to build!

As a rule- do not buy anything that already has drilled holes or obvious dimples / half drilled holes.

If its a company that has been around for a while, and you can google some good feedback on them, then dont give yourself analysis paralysis on what you can buy or not.
According to the ATF, if you walk past the plumbing isle at home depot, you see some nice looking pipes and fittings, and the thought crosses your mind "I wonder if I could turn that into a suppressor..." well then you have already committed a felony by act of "intent".

Yes, the ATF is that ridiculously retarded! Will they ever have a case or be able to substantiate anything in court based on that intent? No! But they are that stupid enough to put it out on a bulletin as a rule. Furthermore, as we have seen recently with the triggers and braces case, ATF does not have authority to make such rules or enforce such rules, which it seems like they pull out of their but*holes, and change the meaning of at whim.

These are not my words, but stating the above on your application has been getting guaranteed approvals as of lately!

Just my personal experience:
I've never done any of the above and have yet to be denied
I've never encouraged others to do the above and they've yet to be denied (have several coworkers and friends I've helped with NFA stuff)

When the ATF asks, I write "All NFA laws to be adhered to before, during, and after approval".

Thank you for the additional input!

Bullshit