I spoke with my realtor again today and she is confident I will be able to get at least 380k out of the house.

Sign a broker agreement that keeps everything confidential and proceed with the contract, disclosures and documents.

So, what I do is add a "% Confidence" column and assign a % value for how confident I am in the estimate based on my experience with that line item.For a line item I'm pretty sure about I might use 90% and for one I'm VERY unsure of I might use 50%. 

You seem Very confident.  Is

I can pretty confidentially say Supply is very very low (at least at this location, read as near airport) hence even interest rates are at 5.5% prices are not coming down and eventually current prices will become the base price.

I currently have a few lenders lined up and 2 realtors I am working with so I am confident I will get a property under contract within the next few months.

I'm also confident I could grow that money faster in Vanguard index funds or something "safe" like this.Thoughts on this method?

I am confident I could do the roof myself to save.

The problem is of course timing and funding mechanism(s).I am confident I can identify RPL1 within 45 days but RPL1 will be more costly than RLN1 net + rehab$, so I will have to find a way to make up the difference.

It is a unique .6 acre lot backing up to a nature preserve that I am not confident I could duplicate at a reasonable cost.