If everything you have read is saying that it is fine, then why does it not feel right for you? Looking around I do get the same impression, it is non-combustible so there is not really a concern there. Basically from what I gather as long as you use the proper wire for use in walls/isolation, leave enough space and generally take good practices in account like using conduit where needed you should be good to go.
I am not an electrician though and certainly not aware of your local code and regulations.
Talking about electricians, if you are worried about doing it not right, why not hire one to do it for you?
I’ve been through 6 electricians and 3 general contractors. Probably more but I can’t keep those numbers straight. They all show up to give a quote then never actually do the work. I’m tired of it.
That being said, the insulation just feels flammable to me. It’s clearly marked otherwise but the paper backing and stuff just made me want to double check
#14 Romex on a 15A breaker is simply not going to get meaningfully hot, even under worst-case scenario loads and even fully insulated in something entirely flammable. If you're very nervous, size it up to #12 -- it will cost slightly more but be even more totally safe. Overbuilding is (should be) the DIYer's creed.
12/2 is what I bought for the basement lights I’m working on. Everything I read said that was the appropriate wire to use so I never even co sidered #14
Make sure you’re buying 14/2 or 12/2 that has a ground wire and running that back to the breaker box. I saw the job you did with the big cable in the floor and it didn’t look like you ran a new cable that had a ground wire. It’s best to replace the old shoddy stuff with circuits that are up to code, even if you’re doing it DIY and your area doesn’t require homeowners to get it inspected. The codes are designed to prevent fires and loss of life.
That was a 240v circuit. It didn’t have a ground because it was 10/3. I had the money to get the stuff with a ground, but they were sold out and I couldn’t get anything for a few weeks so I went with the no ground but it is still up to code and manufacturer approved.
This does have a ground and black is going to the breaker with white and ground going to the ground bar.