Need some advice on interacting with builders

Ok, straight up, I have mild autism and I have little to no experience talking to or hiring builders. Pretty much every interaction I've had with tradespeople has ended up with me getting ripped off, or narrowly avoiding it, in some form or other. I don't have a dad I can ask for advice on this.

I need some help finding a builder to do some , safety remediation, wall restoration, fire compartmentation and (in a later phase) joist sistering in my loft (Victorian terraced house owned by me, Southwest UK.) I've already found a Structural Engineer who has assessed and reported on what needs doing. I've written a 12 page spec for step by step how to do the first phase of the work, as far as I can make out from the advice of the SE (I've leant on a lot of advice from AI for this, corrected with common sense.)

I need a bit of a steer on how much to send to different builders to try and attract them to want to take the job on. AI has suggested things like sending the 12 page spec up front because builders like clear instructions, or being very clear in asking to see their insurance documents etc. but I'm a bit hesitant as to whether this is typically accepted etiquette for builders.

I already know not to use Checkatrade and the like, and I'm trying to stick to FMB builders. I can't get recommendations from other locals because people are pretty cagey giving them out when they have their own work doing (one guy I knew flat out said it took him 3 years to find a decent builder, so he didn't want to share him around).

Any advice on finding someone please?